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[PATCH v18 00/42] DEPT(DEPendency Tracker)

by Byungchul Park

I'm happy to see that DEPT reported real problems in practice: https://lore.kernel.org/lkml/6383cde5-cf4b-facf-6e07-1378a485657d@I-love.SA… https://lore.kernel.org/lkml/1674268856-31807-1-git-send-email-byungchul.pa… https://lore.kernel.org/all/b6e00e77-4a8c-4e05-ab79-266bf05fcc2d@igalia.com/ I’ve added documentation describing DEPT — this should help you understand what DEPT is and how it works. You can use DEPT simply by enabling CONFIG_DEPT and checking dmesg at runtime. --- Hi Linus and folks, I’ve been developing a tool to detect deadlock possibilities by tracking waits/events — rather than lock acquisition order — to cover all the synchronization mechanisms. To summarize the design rationale, starting from the problem statement, through analysis, to the solution: CURRENT STATUS -------------- Lockdep tracks lock acquisition order to identify deadlock conditions. Additionally, it tracks IRQ state changes — via {en,dis}able — to detect cases where locks are acquired unintentionally during interrupt handling. PROBLEM ------- Waits and their associated events that are never reachable can eventually lead to deadlocks. However, since Lockdep focuses solely on lock acquisition order, it has inherent limitations when handling waits and events. Moreover, by tracking only lock acquisition order, Lockdep cannot properly handle read locks or cross-event scenarios — such as wait_for_completion() and complete() — making it increasingly inadequate as a general-purpose deadlock detection tool. SOLUTION -------- Once again, waits and their associated events that are never reachable can eventually lead to deadlocks. The new solution, DEPT, focuses directly on waits and events. DEPT monitors waits and events, and reports them when any become unreachable. DEPT provides: * Correct handling of read locks. * Support for general waits and events. * Continuous operation, even after multiple reports. * Simple, intuitive annotation APIs. There are still false positives, and some are already being worked on for suppression. Especially splitting the folio class into several appropriate classes e.g. block device mapping class and regular file mapping class, is currently under active development by me and Yeoreum Yun. Anyway, these efforts will need to continue for a while, as we’ve seen with lockdep over two decades. DEPT is tagged as EXPERIMENTAL in Kconfig — meaning it’s not yet suitable for use as an automation tool. However, for those who are interested in using DEPT to analyze complex synchronization patterns and extract dependency insights, DEPT would be a great tool for the purpose. Thanks for your support and contributions to: Harry Yoo <harry.yoo(a)oracle.com> Gwan-gyeong Mun <gwan-gyeong.mun(a)intel.com> Yunseong Kim <ysk(a)kzalloc.com> Yeoreum Yun <yeoreum.yun(a)arm.com> FAQ --- Q. Is this the first attempt to solve this problem? A. No. The cross-release feature (commit b09be676e0ff2) attempted to address it — as a Lockdep extension. It was merged, but quickly reverted, because: While it uncovered valuable hidden issues, it also introduced false positives. Since these false positives mask further real problems with Lockdep — and developers strongly dislike them — the feature was rolled back. Q. Why wasn’t DEPT built as a Lockdep extension? A. Lockdep is the result of years of work by kernel developers — and is now very stable. But I chose to build DEPT separately, because: While reusing BFS(Breadth First Search) and Lockdep’s hashing is beneficial, the rest of the system must be rebuilt from scratch to align with DEPT’s wait-event model — since Lockdep was originally designed for tracking lock acquisition orders, not wait-event dependencies. Q. Do you plan to replace Lockdep entirely? A. Not at all — Lockdep still plays a vital role in validating correct lock usage. While its dependency-checking logic should eventually be superseded by DEPT, the rest of its functionality should stay. Q. Should we replace the dependency check immediately? A. Absolutely not. Lockdep’s stability is the result of years of hard work by kernel developers. Lockdep and DEPT should run side by side until DEPT matures. Q. Stronger detection often leads to more false positives — which was a major pain point when cross-release was added. Is DEPT designed to handle this? A. Yes. DEPT’s simple, generalized design enables flexible reporting — so while false positives still need fixing, they’re far less disruptive than they were under the Lockdep extension, cross-release. Q. Why not fix all false positives out-of-tree before merging? A. Since the affected subsystems span the entire kernel, like Lockdep, which has relied on annotations to avoid false positives over the last two decades, DEPT too will require the annotation efforts. Performing annotation work within the mainline will help us add annotations more appropriately and will also make DEPT a useful tool for a wider range of users more quickly. CONFIG_DEPT is marked EXPERIMENTAL, so it’s opt-in. Some users are already interested in using DEPT to analyze complex synchronization patterns and extract dependency insights. Byungchul --- Changes from v17: 1. Rebase on the mainline as of 2025 Dec 5. 2. Convert the documents' format from txt to rst. (feedbacked by Jonathan Corbet and Bagas Sanjaya) 3. Move the documents from 'Documentation/dependency' to 'Documentation/dev-tools'. (feedbakced by Jonathan Corbet) 4. Improve the documentation. (feedbacked by NeilBrown) 5. Use a common function, enter_from_user_mode(), instead of arch specific code, to notice context switch from user mode. (feedbacked by Dave Hansen, Mark Rutland, and Mark Brown) 6. Resolve the header dependency issue by using dept's internal header, instead of relocating 'struct llist_{head,node}' to another header. (feedbacked by Greg KH) 7. Improve page(or folio) usage type APIs. 8. Add rust helper for wait_for_completion(). (feedbacked by Guangbo Cui, Boqun Feng, and Danilo Krummrich) 9. Refine some commit messages. Changes from v16: 1. Rebase on v6.17. 2. Fix a false positive from rcu (by Yunseong Kim) 3. Introduce APIs to set page's usage, dept_set_page_usage() and dept_reset_page_usage() to avoid false positives. 4. Consider lock_page() as a potential wait unconditionally. 5. Consider folio_lock_killable() as a potential wait unconditionally. 6. Add support for tracking PG_writeback waits and events. 7. Fix two build errors due to the additional debug information added by dept. (by Yunseong Kim) Changes from v15: 1. Fix typo and improve comments and commit messages (feedbacked by ALOK TIWARI, Waiman Long, and kernel test robot). 2. Do not stop dept on detection of cicular dependency of recover event, allowing to keep reporting. 3. Add SK hynix to copyright. 4. Consider folio_lock() as a potential wait unconditionally. 5. Fix Kconfig dependency bug (feedbacked by kernel test rebot). 6. Do not suppress reports that involve classes even that have already involved in other reports, allowing to keep reporting. Changes from v14: 1. Rebase on the current latest, v6.15-rc6. 2. Refactor dept code. 3. With multi event sites for a single wait, even if an event forms a circular dependency, the event can be recovered by other event(or wake up) paths. Even though informing the circular dependency is worthy but it should be suppressed once informing it, if it doesn't lead an actual deadlock. So introduce APIs to annotate the relationship between event site and recover site, that are, event_site() and dept_recover_event(). 4. wait_for_completion() worked with dept map embedded in struct completion. However, it generates a few false positves since all the waits using the instance of struct completion, share the map and key. To avoid the false positves, make it not to share the map and key but each wait_for_completion() caller have its own key by default. Of course, external maps also can be used if needed. 5. Fix a bug about hardirq on/off tracing. 6. Implement basic unit test for dept. 7. Add more supports for dma fence synchronization. 8. Add emergency stop of dept e.g. on panic(). 9. Fix false positives by mmu_notifier_invalidate_*(). 10. Fix recursive call bug by DEPT_WARN_*() and DEPT_STOP(). 11. Fix trivial bugs in DEPT_WARN_*() and DEPT_STOP(). 12. Fix a bug that a spin lock, dept_pool_spin, is used in both contexts of irq disabled and enabled without irq disabled. 13. Suppress reports with classes, any of that already have been reported, even though they have different chains but being barely meaningful. 14. Print stacktrace of the wait that an event is now waking up, not only stacktrace of the event. 15. Make dept aware of lockdep_cmp_fn() that is used to avoid false positives in lockdep so that dept can also avoid them. 16. Do do_event() only if there are no ecxts have been delimited. 17. Fix a bug that was not synchronized for stage_m in struct dept_task, using a spin lock, dept_task()->stage_lock. 18. Fix a bug that dept didn't handle the case that multiple ttwus for a single waiter can be called at the same time e.i. a race issue. 19. Distinguish each kernel context from others, not only by system call but also by user oriented fault so that dept can work with more accuracy information about kernel context. That helps to avoid a few false positives. 20. Limit dept's working to x86_64 and arm64. Changes from v13: 1. Rebase on the current latest version, v6.9-rc7. 2. Add 'dept' documentation describing dept APIs. Changes from v12: 1. Refine the whole document for dept. 2. Add 'Interpret dept report' section in the document, using a deadlock report obtained in practice. Hope this version of document helps guys understand dept better. https://lore.kernel.org/lkml/6383cde5-cf4b-facf-6e07-1378a485657d@I-love.SA… https://lore.kernel.org/lkml/1674268856-31807-1-git-send-email-byungchul.pa… Changes from v11: 1. Add 'dept' documentation describing the concept of dept. 2. Rewrite the commit messages of the following commits for using weaker lockdep annotation, for better description. fs/jbd2: Use a weaker annotation in journal handling cpu/hotplug: Use a weaker annotation in AP thread (feedbacked by Thomas Gleixner) Changes from v10: 1. Fix noinstr warning when building kernel source. 2. dept has been reporting some false positives due to the folio lock's unfairness. Reflect it and make dept work based on dept annotaions instead of just wait and wake up primitives. 3. Remove the support for PG_writeback while working on 2. I will add the support later if needed. 4. dept didn't print stacktrace for [S] if the participant of a deadlock is not lock mechanism but general wait and event. However, it made hard to interpret the report in that case. So add support to print stacktrace of the requestor who asked the event context to run - usually a waiter of the event does it just before going to wait state. 5. Give up tracking raw_local_irq_{disable,enable}() since it totally messed up dept's irq tracking. So make it work in the same way as lockdep does. I will consider it once any false positives by those are observed again. 6. Change the manual rwsem_acquire_read(->j_trans_commit_map) annotation in fs/jbd2/transaction.c to the try version so that it works as much as it exactly needs. 7. Remove unnecessary 'inline' keyword in dept.c and add '__maybe_unused' to a needed place. Changes from v9: 1. Fix a bug. SDT tracking didn't work well because of my big mistake that I should've used waiter's map to indentify its class but it had been working with waker's one. FYI, PG_locked and PG_writeback weren't affected. They still worked well. (reported by YoungJun) Changes from v8: 1. Fix build error by adding EXPORT_SYMBOL(PG_locked_map) and EXPORT_SYMBOL(PG_writeback_map) for kernel module build - appologize for that. (reported by kernel test robot) 2. Fix build error by removing header file's circular dependency that was caused by "atomic.h", "kernel.h" and "irqflags.h", which I introduced - appolgize for that. (reported by kernel test robot) Changes from v7: 1. Fix a bug that cannot track rwlock dependency properly, introduced in v7. (reported by Boqun and lockdep selftest) 2. Track wait/event of PG_{locked,writeback} more aggressively assuming that when a bit of PG_{locked,writeback} is cleared there might be waits on the bit. (reported by Linus, Hillf and syzbot) 3. Fix and clean bad style code e.i. unnecessarily introduced a randome pattern and so on. (pointed out by Linux) 4. Clean code for applying dept to wait_for_completion(). Changes from v6: 1. Tie to task scheduler code to track sleep and try_to_wake_up() assuming sleeps cause waits, try_to_wake_up()s would be the events that those are waiting for, of course with proper dept annotations, sdt_might_sleep_weak(), sdt_might_sleep_strong() and so on. For these cases, class is classified at sleep entrance rather than the synchronization initialization code. Which would extremely reduce false alarms. 2. Remove the dept associated instance in each page struct for tracking dependencies by PG_locked and PG_writeback thanks to the 1. work above. 3. Introduce CONFIG_dept_AGGRESIVE_TIMEOUT_WAIT to suppress reports that waits with timeout set are involved, for those who don't like verbose reporting. 4. Add a mechanism to refill the internal memory pools on running out so that dept could keep working as long as free memory is available in the system. 5. Re-enable tracking hashed-waitqueue wait. That's going to no longer generate false positives because class is classified at sleep entrance rather than the waitqueue initailization. 6. Refactor to make it easier to port onto each new version of the kernel. 7. Apply dept to dma fence. 8. Do trivial optimizaitions. Changes from v5: 1. Use just pr_warn_once() rather than WARN_ONCE() on the lack of internal resources because WARN_*() printing stacktrace is too much for informing the lack. (feedback from Ted, Hyeonggon) 2. Fix trivial bugs like missing initializing a struct before using it. 3. Assign a different class per task when handling onstack variables for waitqueue or the like. Which makes dept distinguish between onstack variables of different tasks so as to prevent false positives. (reported by Hyeonggon) 4. Make dept aware of even raw_local_irq_*() to prevent false positives. (reported by Hyeonggon) 5. Don't consider dependencies between the events that might be triggered within __schedule() and the waits that requires __schedule(), real ones. (reported by Hyeonggon) 6. Unstage the staged wait that has prepare_to_wait_event()'ed *and* yet to get to __schedule(), if we encounter __schedule() in-between for another sleep, which is possible if e.g. a mutex_lock() exists in 'condition' of ___wait_event(). 7. Turn on CONFIG_PROVE_LOCKING when CONFIG_DEPT is on, to rely on the hardirq and softirq entrance tracing to make dept more portable for now. Changes from v4: 1. Fix some bugs that produce false alarms. 2. Distinguish each syscall context from another *for arm64*. 3. Make it not warn it but just print it in case dept ring buffer gets exhausted. (feedback from Hyeonggon) 4. Explicitely describe "EXPERIMENTAL" and "dept might produce false positive reports" in Kconfig. (feedback from Ted) Changes from v3: 1. dept shouldn't create dependencies between different depths of a class that were indicated by *_lock_nested(). dept normally doesn't but it does once another lock class comes in. So fixed it. (feedback from Hyeonggon) 2. dept considered a wait as a real wait once getting to __schedule() even if it has been set to TASK_RUNNING by wake up sources in advance. Fixed it so that dept doesn't consider the case as a real wait. (feedback from Jan Kara) 3. Stop tracking dependencies with a map once the event associated with the map has been handled. dept will start to work with the map again, on the next sleep. Changes from v2: 1. Disable dept on bit_wait_table[] in sched/wait_bit.c reporting a lot of false positives, which is my fault. Wait/event for bit_wait_table[] should've been tagged in a higher layer for better work, which is a future work. (feedback from Jan Kara) 2. Disable dept on crypto_larval's completion to prevent a false positive. Changes from v1: 1. Fix coding style and typo. (feedback from Steven) 2. Distinguish each work context from another in workqueue. 3. Skip checking lock acquisition with nest_lock, which is about correct lock usage that should be checked by lockdep. Changes from RFC(v0): 1. Prevent adding a wait tag at prepare_to_wait() but __schedule(). (feedback from Linus and Matthew) 2. Use try version at lockdep_acquire_cpus_lock() annotation. 3. Distinguish each syscall context from another. Byungchul Park (41): dept: implement DEPT(DEPendency Tracker) dept: add single event dependency tracker APIs dept: add lock dependency tracker APIs dept: tie to lockdep and IRQ tracing dept: add proc knobs to show stats and dependency graph dept: distinguish each kernel context from another dept: distinguish each work from another dept: add a mechanism to refill the internal memory pools on running out dept: record the latest one out of consecutive waits of the same class dept: apply sdt_might_sleep_{start,end}() to wait_for_completion()/complete() dept: apply sdt_might_sleep_{start,end}() to swait dept: apply sdt_might_sleep_{start,end}() to waitqueue wait dept: apply sdt_might_sleep_{start,end}() to hashed-waitqueue wait dept: apply sdt_might_sleep_{start,end}() to dma fence dept: track timeout waits separately with a new Kconfig dept: apply timeout consideration to wait_for_completion()/complete() dept: apply timeout consideration to swait dept: apply timeout consideration to waitqueue wait dept: apply timeout consideration to hashed-waitqueue wait dept: apply timeout consideration to dma fence wait dept: make dept able to work with an external wgen dept: track PG_locked with dept dept: print staged wait's stacktrace on report locking/lockdep: prevent various lockdep assertions when lockdep_off()'ed dept: add documents for dept cpu/hotplug: use a weaker annotation in AP thread dept: assign dept map to mmu notifier invalidation synchronization dept: assign unique dept_key to each distinct dma fence caller dept: make dept aware of lockdep_set_lock_cmp_fn() annotation dept: make dept stop from working on debug_locks_off() dept: assign unique dept_key to each distinct wait_for_completion() caller completion, dept: introduce init_completion_dmap() API dept: introduce a new type of dependency tracking between multi event sites dept: add module support for struct dept_event_site and dept_event_site_dep dept: introduce event_site() to disable event tracking if it's recoverable dept: implement a basic unit test for dept dept: call dept_hardirqs_off() in local_irq_*() regardless of irq state dept: introduce APIs to set page usage and use subclasses_evt for the usage dept: track PG_writeback with dept SUNRPC: relocate struct rcu_head to the first field of struct rpc_xprt mm: percpu: increase PERCPU_DYNAMIC_SIZE_SHIFT on DEPT and large PAGE_SIZE Yunseong Kim (1): rcu/update: fix same dept key collision between various types of RCU Documentation/dev-tools/dept.rst | 778 ++++++ Documentation/dev-tools/dept_api.rst | 125 + drivers/dma-buf/dma-fence.c | 23 +- include/asm-generic/vmlinux.lds.h | 13 +- include/linux/completion.h | 124 +- include/linux/dept.h | 402 +++ include/linux/dept_ldt.h | 78 + include/linux/dept_sdt.h | 68 + include/linux/dept_unit_test.h | 67 + include/linux/dma-fence.h | 74 +- include/linux/hardirq.h | 3 + include/linux/irq-entry-common.h | 4 + include/linux/irqflags.h | 21 +- include/linux/local_lock_internal.h | 1 + include/linux/lockdep.h | 105 +- include/linux/lockdep_types.h | 3 + include/linux/mm_types.h | 4 + include/linux/mmu_notifier.h | 26 + include/linux/module.h | 5 + include/linux/mutex.h | 1 + include/linux/page-flags.h | 217 +- include/linux/pagemap.h | 37 +- include/linux/percpu-rwsem.h | 2 +- include/linux/percpu.h | 4 + include/linux/rcupdate_wait.h | 13 +- include/linux/rtmutex.h | 1 + include/linux/rwlock_types.h | 1 + include/linux/rwsem.h | 1 + include/linux/sched.h | 118 + include/linux/seqlock.h | 2 +- include/linux/spinlock_types_raw.h | 3 + include/linux/srcu.h | 2 +- include/linux/sunrpc/xprt.h | 9 +- include/linux/swait.h | 3 + include/linux/wait.h | 3 + include/linux/wait_bit.h | 3 + init/init_task.c | 2 + init/main.c | 2 + kernel/Makefile | 1 + kernel/cpu.c | 2 +- kernel/dependency/Makefile | 5 + kernel/dependency/dept.c | 3499 ++++++++++++++++++++++++++ kernel/dependency/dept_hash.h | 10 + kernel/dependency/dept_internal.h | 314 +++ kernel/dependency/dept_object.h | 13 + kernel/dependency/dept_proc.c | 94 + kernel/dependency/dept_unit_test.c | 173 ++ kernel/exit.c | 1 + kernel/fork.c | 2 + kernel/locking/lockdep.c | 33 + kernel/module/main.c | 19 + kernel/rcu/rcu.h | 1 + kernel/rcu/update.c | 5 +- kernel/sched/completion.c | 62 +- kernel/sched/core.c | 9 + kernel/workqueue.c | 3 + lib/Kconfig.debug | 48 + lib/debug_locks.c | 2 + lib/locking-selftest.c | 2 + mm/filemap.c | 38 + mm/mm_init.c | 3 + mm/mmu_notifier.c | 31 +- rust/helpers/completion.c | 5 + 63 files changed, 6602 insertions(+), 121 deletions(-) create mode 100644 Documentation/dev-tools/dept.rst create mode 100644 Documentation/dev-tools/dept_api.rst create mode 100644 include/linux/dept.h create mode 100644 include/linux/dept_ldt.h create mode 100644 include/linux/dept_sdt.h create mode 100644 include/linux/dept_unit_test.h create mode 100644 kernel/dependency/Makefile create mode 100644 kernel/dependency/dept.c create mode 100644 kernel/dependency/dept_hash.h create mode 100644 kernel/dependency/dept_internal.h create mode 100644 kernel/dependency/dept_object.h create mode 100644 kernel/dependency/dept_proc.c create mode 100644 kernel/dependency/dept_unit_test.c base-commit: 43dfc13ca972988e620a6edb72956981b75ab6b0 -- 2.17.1

1 month, 1 week

Re: Unlocking Wordplay: A Guide to the Connections Game

by one slopalice

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1 month, 1 week

[PATCH v2] dma-buf: remove unused dma-fence-unwrap.c (stable/linux-5.15.y only)

by Tudor Ambarus

The file drivers/dma-buf/dma-fence-unwrap.c was incorrectly added to the 5.15.y stable branch in commit 4e82b9c11d3c ("dma-buf: add dma_fence_timestamp helper") as a new file, but it was never enabled in the Makefile, and its header include/linux/dma-fence-unwrap.h was not present, making it uncompilable. A full revert of commit 4e82b9c11d3c ("dma-buf: add dma_fence_timestamp helper") is not desirable because that commit also introduced the valid dma_fence_timestamp() helper and fixed legitimate timestamp race windows in drivers/dma-buf/sync_file.c and drivers/gpu/drm/scheduler/sched_main.c. Since there are no users of dma-fence-unwrap in the 5.15.y branch, remove the unused file to clean up the tree and avoid confusion. Fixes: 4e82b9c11d3c ("dma-buf: add dma_fence_timestamp helper") Signed-off-by: Tudor Ambarus <tudor.ambarus(a)linaro.org> --- Changes in v2: - add To: stable(a)vger.kernel.org - Link to v1: https://lore.kernel.org/r/20260703-5-15-dma-fence-unwrap-v1-1-0cf644bc501f@… --- drivers/dma-buf/dma-fence-unwrap.c | 176 ------------------------------------- 1 file changed, 176 deletions(-) diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c deleted file mode 100644 index 628af51c81af..000000000000 --- a/drivers/dma-buf/dma-fence-unwrap.c +++ /dev/null @@ -1,176 +0,0 @@ -// SPDX-License-Identifier: GPL-2.0-only -/* - * dma-fence-util: misc functions for dma_fence objects - * - * Copyright (C) 2022 Advanced Micro Devices, Inc. - * Authors: - * Christian König <christian.koenig(a)amd.com> - */ - -#include <linux/dma-fence.h> -#include <linux/dma-fence-array.h> -#include <linux/dma-fence-chain.h> -#include <linux/dma-fence-unwrap.h> -#include <linux/slab.h> - -/* Internal helper to start new array iteration, don't use directly */ -static struct dma_fence * -__dma_fence_unwrap_array(struct dma_fence_unwrap *cursor) -{ - cursor->array = dma_fence_chain_contained(cursor->chain); - cursor->index = 0; - return dma_fence_array_first(cursor->array); -} - -/** - * dma_fence_unwrap_first - return the first fence from fence containers - * @head: the entrypoint into the containers - * @cursor: current position inside the containers - * - * Unwraps potential dma_fence_chain/dma_fence_array containers and return the - * first fence. - */ -struct dma_fence *dma_fence_unwrap_first(struct dma_fence *head, - struct dma_fence_unwrap *cursor) -{ - cursor->chain = dma_fence_get(head); - return __dma_fence_unwrap_array(cursor); -} -EXPORT_SYMBOL_GPL(dma_fence_unwrap_first); - -/** - * dma_fence_unwrap_next - return the next fence from a fence containers - * @cursor: current position inside the containers - * - * Continue unwrapping the dma_fence_chain/dma_fence_array containers and return - * the next fence from them. - */ -struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor) -{ - struct dma_fence *tmp; - - ++cursor->index; - tmp = dma_fence_array_next(cursor->array, cursor->index); - if (tmp) - return tmp; - - cursor->chain = dma_fence_chain_walk(cursor->chain); - return __dma_fence_unwrap_array(cursor); -} -EXPORT_SYMBOL_GPL(dma_fence_unwrap_next); - -/* Implementation for the dma_fence_merge() marco, don't use directly */ -struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences, - struct dma_fence **fences, - struct dma_fence_unwrap *iter) -{ - struct dma_fence_array *result; - struct dma_fence *tmp, **array; - ktime_t timestamp; - unsigned int i; - size_t count; - - count = 0; - timestamp = ns_to_ktime(0); - for (i = 0; i < num_fences; ++i) { - dma_fence_unwrap_for_each(tmp, &iter[i], fences[i]) { - if (!dma_fence_is_signaled(tmp)) { - ++count; - } else { - ktime_t t = dma_fence_timestamp(tmp); - - if (ktime_after(t, timestamp)) - timestamp = t; - } - } - } - - /* - * If we couldn't find a pending fence just return a private signaled - * fence with the timestamp of the last signaled one. - */ - if (count == 0) - return dma_fence_allocate_private_stub(timestamp); - - array = kmalloc_array(count, sizeof(*array), GFP_KERNEL); - if (!array) - return NULL; - - /* - * This trashes the input fence array and uses it as position for the - * following merge loop. This works because the dma_fence_merge() - * wrapper macro is creating this temporary array on the stack together - * with the iterators. - */ - for (i = 0; i < num_fences; ++i) - fences[i] = dma_fence_unwrap_first(fences[i], &iter[i]); - - count = 0; - do { - unsigned int sel; - -restart: - tmp = NULL; - for (i = 0; i < num_fences; ++i) { - struct dma_fence *next; - - while (fences[i] && dma_fence_is_signaled(fences[i])) - fences[i] = dma_fence_unwrap_next(&iter[i]); - - next = fences[i]; - if (!next) - continue; - - /* - * We can't guarantee that inpute fences are ordered by - * context, but it is still quite likely when this - * function is used multiple times. So attempt to order - * the fences by context as we pass over them and merge - * fences with the same context. - */ - if (!tmp || tmp->context > next->context) { - tmp = next; - sel = i; - - } else if (tmp->context < next->context) { - continue; - - } else if (dma_fence_is_later(tmp, next)) { - fences[i] = dma_fence_unwrap_next(&iter[i]); - goto restart; - } else { - fences[sel] = dma_fence_unwrap_next(&iter[sel]); - goto restart; - } - } - - if (tmp) { - array[count++] = dma_fence_get(tmp); - fences[sel] = dma_fence_unwrap_next(&iter[sel]); - } - } while (tmp); - - if (count == 0) { - tmp = dma_fence_allocate_private_stub(ktime_get()); - goto return_tmp; - } - - if (count == 1) { - tmp = array[0]; - goto return_tmp; - } - - result = dma_fence_array_create(count, array, - dma_fence_context_alloc(1), - 1, false); - if (!result) { - tmp = NULL; - goto return_tmp; - } - return &result->base; - -return_tmp: - kfree(array); - return tmp; -} -EXPORT_SYMBOL_GPL(__dma_fence_unwrap_merge); --- base-commit: eceeec79dbc646d6dace49ed1ba2f656683d5537 change-id: 20260703-5-15-dma-fence-unwrap-0f4a6c03daf2 Best regards, -- Tudor Ambarus <tudor.ambarus(a)linaro.org>

1 month, 1 week

[PATCH] dma-buf: remove unused dma-fence-unwrap.c (stable/linux-5.15.y only)

by Tudor Ambarus

The file drivers/dma-buf/dma-fence-unwrap.c was incorrectly added to the 5.15.y stable branch in commit 4e82b9c11d3c ("dma-buf: add dma_fence_timestamp helper") as a new file, but it was never enabled in the Makefile, and its header include/linux/dma-fence-unwrap.h was not present, making it uncompilable. A full revert of commit 4e82b9c11d3c ("dma-buf: add dma_fence_timestamp helper") is not desirable because that commit also introduced the valid dma_fence_timestamp() helper and fixed legitimate timestamp race windows in drivers/dma-buf/sync_file.c and drivers/gpu/drm/scheduler/sched_main.c. Since there are no users of dma-fence-unwrap in the 5.15.y branch, remove the unused file to clean up the tree and avoid confusion. Fixes: 4e82b9c11d3c ("dma-buf: add dma_fence_timestamp helper") Signed-off-by: Tudor Ambarus <tudor.ambarus(a)linaro.org> --- drivers/dma-buf/dma-fence-unwrap.c | 176 ------------------------------------- 1 file changed, 176 deletions(-) diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c deleted file mode 100644 index 628af51c81af..000000000000 --- a/drivers/dma-buf/dma-fence-unwrap.c +++ /dev/null @@ -1,176 +0,0 @@ -// SPDX-License-Identifier: GPL-2.0-only -/* - * dma-fence-util: misc functions for dma_fence objects - * - * Copyright (C) 2022 Advanced Micro Devices, Inc. - * Authors: - * Christian König <christian.koenig(a)amd.com> - */ - -#include <linux/dma-fence.h> -#include <linux/dma-fence-array.h> -#include <linux/dma-fence-chain.h> -#include <linux/dma-fence-unwrap.h> -#include <linux/slab.h> - -/* Internal helper to start new array iteration, don't use directly */ -static struct dma_fence * -__dma_fence_unwrap_array(struct dma_fence_unwrap *cursor) -{ - cursor->array = dma_fence_chain_contained(cursor->chain); - cursor->index = 0; - return dma_fence_array_first(cursor->array); -} - -/** - * dma_fence_unwrap_first - return the first fence from fence containers - * @head: the entrypoint into the containers - * @cursor: current position inside the containers - * - * Unwraps potential dma_fence_chain/dma_fence_array containers and return the - * first fence. - */ -struct dma_fence *dma_fence_unwrap_first(struct dma_fence *head, - struct dma_fence_unwrap *cursor) -{ - cursor->chain = dma_fence_get(head); - return __dma_fence_unwrap_array(cursor); -} -EXPORT_SYMBOL_GPL(dma_fence_unwrap_first); - -/** - * dma_fence_unwrap_next - return the next fence from a fence containers - * @cursor: current position inside the containers - * - * Continue unwrapping the dma_fence_chain/dma_fence_array containers and return - * the next fence from them. - */ -struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor) -{ - struct dma_fence *tmp; - - ++cursor->index; - tmp = dma_fence_array_next(cursor->array, cursor->index); - if (tmp) - return tmp; - - cursor->chain = dma_fence_chain_walk(cursor->chain); - return __dma_fence_unwrap_array(cursor); -} -EXPORT_SYMBOL_GPL(dma_fence_unwrap_next); - -/* Implementation for the dma_fence_merge() marco, don't use directly */ -struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences, - struct dma_fence **fences, - struct dma_fence_unwrap *iter) -{ - struct dma_fence_array *result; - struct dma_fence *tmp, **array; - ktime_t timestamp; - unsigned int i; - size_t count; - - count = 0; - timestamp = ns_to_ktime(0); - for (i = 0; i < num_fences; ++i) { - dma_fence_unwrap_for_each(tmp, &iter[i], fences[i]) { - if (!dma_fence_is_signaled(tmp)) { - ++count; - } else { - ktime_t t = dma_fence_timestamp(tmp); - - if (ktime_after(t, timestamp)) - timestamp = t; - } - } - } - - /* - * If we couldn't find a pending fence just return a private signaled - * fence with the timestamp of the last signaled one. - */ - if (count == 0) - return dma_fence_allocate_private_stub(timestamp); - - array = kmalloc_array(count, sizeof(*array), GFP_KERNEL); - if (!array) - return NULL; - - /* - * This trashes the input fence array and uses it as position for the - * following merge loop. This works because the dma_fence_merge() - * wrapper macro is creating this temporary array on the stack together - * with the iterators. - */ - for (i = 0; i < num_fences; ++i) - fences[i] = dma_fence_unwrap_first(fences[i], &iter[i]); - - count = 0; - do { - unsigned int sel; - -restart: - tmp = NULL; - for (i = 0; i < num_fences; ++i) { - struct dma_fence *next; - - while (fences[i] && dma_fence_is_signaled(fences[i])) - fences[i] = dma_fence_unwrap_next(&iter[i]); - - next = fences[i]; - if (!next) - continue; - - /* - * We can't guarantee that inpute fences are ordered by - * context, but it is still quite likely when this - * function is used multiple times. So attempt to order - * the fences by context as we pass over them and merge - * fences with the same context. - */ - if (!tmp || tmp->context > next->context) { - tmp = next; - sel = i; - - } else if (tmp->context < next->context) { - continue; - - } else if (dma_fence_is_later(tmp, next)) { - fences[i] = dma_fence_unwrap_next(&iter[i]); - goto restart; - } else { - fences[sel] = dma_fence_unwrap_next(&iter[sel]); - goto restart; - } - } - - if (tmp) { - array[count++] = dma_fence_get(tmp); - fences[sel] = dma_fence_unwrap_next(&iter[sel]); - } - } while (tmp); - - if (count == 0) { - tmp = dma_fence_allocate_private_stub(ktime_get()); - goto return_tmp; - } - - if (count == 1) { - tmp = array[0]; - goto return_tmp; - } - - result = dma_fence_array_create(count, array, - dma_fence_context_alloc(1), - 1, false); - if (!result) { - tmp = NULL; - goto return_tmp; - } - return &result->base; - -return_tmp: - kfree(array); - return tmp; -} -EXPORT_SYMBOL_GPL(__dma_fence_unwrap_merge); --- base-commit: eceeec79dbc646d6dace49ed1ba2f656683d5537 change-id: 20260703-5-15-dma-fence-unwrap-0f4a6c03daf2 Best regards, -- Tudor Ambarus <tudor.ambarus(a)linaro.org>

1 month, 2 weeks

[PATCH] dma-buf: docs: remove invalid struct member

by Nicolás Antinori

In the structs dma_fence_array and dma_fence_chain, the field 'lock' has been removed, but its documentation comment remained. Remove the stale descriptions to clear up the following kernel-doc warnings: WARNING: ./include/linux/dma-fence-array.h:47 Excess struct member 'lock' description in 'dma_fence_array' WARNING: ./include/linux/dma-fence-array.h:47 Excess struct member 'lock' description in 'dma_fence_array' WARNING: ./include/linux/dma-fence-chain.h:48 Excess struct member 'lock' description in 'dma_fence_chain' WARNING: ./include/linux/dma-fence-chain.h:48 Excess struct member 'lock' description in 'dma_fence_chain' Fixes: 5943243914b9 ("dma-buf: use inline lock for the dma-fence-array") Fixes: a408c0ca0c41 ("dma-buf: use inline lock for the dma-fence-chain") Signed-off-by: Nicolás Antinori <nico.antinori.7(a)gmail.com> --- include/linux/dma-fence-array.h | 1 - include/linux/dma-fence-chain.h | 1 - 2 files changed, 2 deletions(-) diff --git a/include/linux/dma-fence-array.h b/include/linux/dma-fence-array.h index 1b1d87579c38..0c49d7ccefb6 100644 --- a/include/linux/dma-fence-array.h +++ b/include/linux/dma-fence-array.h @@ -28,7 +28,6 @@ struct dma_fence_array_cb { /** * struct dma_fence_array - fence to represent an array of fences * @base: fence base class - * @lock: spinlock for fence handling * @num_fences: number of fences in the array * @num_pending: fences in the array still pending * @fences: array of the fences diff --git a/include/linux/dma-fence-chain.h b/include/linux/dma-fence-chain.h index df3beadf1515..42289f505164 100644 --- a/include/linux/dma-fence-chain.h +++ b/include/linux/dma-fence-chain.h @@ -20,7 +20,6 @@ * @prev: previous fence of the chain * @prev_seqno: original previous seqno before garbage collection * @fence: encapsulated fence - * @lock: spinlock for fence handling */ struct dma_fence_chain { struct dma_fence base; -- 2.47.3

1 month, 2 weeks

[PATCH] dma-buf: Split sgl by largest page-aligned chunk

by David Hu

Currently, `fill_sg_entry()` splits the scatterlist using `UINT_MAX`. This creates a non-page-aligned DMA length (`0xFFFFFFFF`) for the first entry, resulting in non-page-aligned DMA addresses for all subsequent entries. While the underlying IOMMU mapping may be contiguous, hardware DMA engines often require explicit address alignment (e.g., page, cacheline, or storage sector boundaries). Passing unaligned addresses and lengths can cause explicit failures in DMA descriptor creation or silent data corruption if lower unaligned bits are truncated. Fix this by splitting the scatterlist by the largest possible page aligned chunk within `UINT_MAX` (`ALIGN_DOWN(UINT_MAX, PAGE_SIZE)`). This ensures all scatterlist DMA addresses and lengths remain page aligned and satisfy hardware constraints. Page-aligned entries allow the system to cleanly chunk payloads into PCIe MaxPayloadSize (MPS) (e.g., 128 bytes, 256 bytes, 512 bytes). As a result, this may help reduce TLP fragmentation in P2P transfers and alleviate potential congestion within a logical PCIe switch partition, especially when Relaxed Ordering is not possible due to hardware constraints. Reported-by: sashiko-bot <sashiko-bot(a)kernel.org> Closes: https://lore.kernel.org/all/20260609165431.778061F00893@smtp.kernel.org/ Fixes: 3aa31a8bb11e ("dma-buf: provide phys_vec to scatter-gather mapping routine") Cc: stable(a)vger.kernel.org Signed-off-by: David Hu <xuehaohu(a)google.com> --- drivers/dma-buf/dma-buf-mapping.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/drivers/dma-buf/dma-buf-mapping.c b/drivers/dma-buf/dma-buf-mapping.c index 794acff2546a..f2bde38fdb1f 100644 --- a/drivers/dma-buf/dma-buf-mapping.c +++ b/drivers/dma-buf/dma-buf-mapping.c @@ -5,6 +5,9 @@ */ #include <linux/dma-buf-mapping.h> #include <linux/dma-resv.h> +#include <linux/align.h> + +#define MAX_ENT_SZ ALIGN_DOWN(UINT_MAX, PAGE_SIZE) static struct scatterlist *fill_sg_entry(struct scatterlist *sgl, size_t length, dma_addr_t addr) @@ -12,9 +15,9 @@ static struct scatterlist *fill_sg_entry(struct scatterlist *sgl, size_t length, unsigned int len, nents; int i; - nents = DIV_ROUND_UP(length, UINT_MAX); + nents = DIV_ROUND_UP(length, MAX_ENT_SZ); for (i = 0; i < nents; i++) { - len = min_t(size_t, length, UINT_MAX); + len = min_t(size_t, length, MAX_ENT_SZ); length -= len; /* * DMABUF abuses scatterlist to create a scatterlist @@ -24,7 +27,7 @@ static struct scatterlist *fill_sg_entry(struct scatterlist *sgl, size_t length, * does not require the CPU list for mapping or unmapping. */ sg_set_page(sgl, NULL, 0, 0); - sg_dma_address(sgl) = addr + (dma_addr_t)i * UINT_MAX; + sg_dma_address(sgl) = addr + (dma_addr_t)i * MAX_ENT_SZ; sg_dma_len(sgl) = len; sgl = sg_next(sgl); } @@ -41,14 +44,14 @@ static unsigned int calc_sg_nents(struct dma_iova_state *state, if (!state || !dma_use_iova(state)) { for (i = 0; i < nr_ranges; i++) - nents += DIV_ROUND_UP(phys_vec[i].len, UINT_MAX); + nents += DIV_ROUND_UP(phys_vec[i].len, MAX_ENT_SZ); } else { /* * In IOVA case, there is only one SG entry which spans * for whole IOVA address space, but we need to make sure * that it fits sg->length, maybe we need more. */ - nents = DIV_ROUND_UP(size, UINT_MAX); + nents = DIV_ROUND_UP(size, MAX_ENT_SZ); } return nents; -- 2.55.0.rc0.738.g0c8ab3ebcc-goog

1 month, 2 weeks

[PATCH] rust: device_id: rename IdTable::as_ptr to as_raw_id_table()

by Alice Ryhl

The current name of `as_ptr` is very generic, and if you attempt to invoke `foo.as_ptr()` on a type for which this method is missing, then an error along these lines will be printed: error[E0599]: no method named `as_ptr` found for reference `&DmaBuf` in the current scope --> linux/rust/kernel/dma_buf/buf.rs:54:38 | 54 | ptr::eq(self.as_ptr(), other.as_ptr()) | ^^^^^^ method not found in `&DmaBuf` | = help: items from traits can only be used if the trait is implemented and in scope note: `device_id::IdTable` defines an item `as_ptr`, perhaps you need to implement it --> linux/rust/kernel/device_id.rs:165:1 | 165 | pub trait IdTable<T: RawDeviceId, U> { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Suggesting the IdTable trait when an as_ptr() method is missing is not useful. Renaming it to `as_raw_id_table` makes the method name unique to this trait and avoids these bad suggestions. Assisted-by: Antigravity:Gemini Signed-off-by: Alice Ryhl <aliceryhl(a)google.com> --- rust/kernel/auxiliary.rs | 2 +- rust/kernel/device_id.rs | 4 ++-- rust/kernel/driver.rs | 8 +++++--- rust/kernel/i2c.rs | 8 ++++---- rust/kernel/pci.rs | 2 +- rust/kernel/platform.rs | 4 ++-- rust/kernel/usb.rs | 2 +- 7 files changed, 16 insertions(+), 14 deletions(-) diff --git a/rust/kernel/auxiliary.rs b/rust/kernel/auxiliary.rs index c42928d5a239..fd6940577e0d 100644 --- a/rust/kernel/auxiliary.rs +++ b/rust/kernel/auxiliary.rs @@ -64,7 +64,7 @@ unsafe fn register( (*adrv.get()).name = name.as_char_ptr(); (*adrv.get()).probe = Some(Self::probe_callback); (*adrv.get()).remove = Some(Self::remove_callback); - (*adrv.get()).id_table = T::ID_TABLE.as_ptr(); + (*adrv.get()).id_table = T::ID_TABLE.as_raw_id_table(); } // SAFETY: `adrv` is guaranteed to be a valid `DriverType`. diff --git a/rust/kernel/device_id.rs b/rust/kernel/device_id.rs index 8e9721446014..821da02540b1 100644 --- a/rust/kernel/device_id.rs +++ b/rust/kernel/device_id.rs @@ -164,7 +164,7 @@ impl<T: RawDeviceId + RawDeviceIdIndex, U, const N: usize> IdArray<T, U, N> { /// `IdArray` doesn't matter. pub trait IdTable<T: RawDeviceId, U> { /// Obtain the pointer to the ID table. - fn as_ptr(&self) -> *const T::RawType; + fn as_raw_id_table(&self) -> *const T::RawType; /// Obtain the pointer to the bus specific device ID from an index. fn id(&self, index: usize) -> &T::RawType; @@ -174,7 +174,7 @@ pub trait IdTable<T: RawDeviceId, U> { } impl<T: RawDeviceId, U, const N: usize> IdTable<T, U> for IdArray<T, U, N> { - fn as_ptr(&self) -> *const T::RawType { + fn as_raw_id_table(&self) -> *const T::RawType { // This cannot be `self.ids.as_ptr()`, as the return pointer must have correct provenance // to access the sentinel. core::ptr::from_ref(self).cast() diff --git a/rust/kernel/driver.rs b/rust/kernel/driver.rs index bf5ba0d27553..69068adcbdae 100644 --- a/rust/kernel/driver.rs +++ b/rust/kernel/driver.rs @@ -341,7 +341,8 @@ fn acpi_id_info(dev: &device::Device) -> Option<&'static Self::IdInfo> { // SAFETY: // - `table` has static lifetime, hence it's valid for read, // - `dev` is guaranteed to be valid while it's alive, and so is `dev.as_raw()`. - let raw_id = unsafe { bindings::acpi_match_device(table.as_ptr(), dev.as_raw()) }; + let raw_id = + unsafe { bindings::acpi_match_device(table.as_raw_id_table(), dev.as_raw()) }; if raw_id.is_null() { None @@ -374,7 +375,8 @@ fn of_id_info(dev: &device::Device) -> Option<&'static Self::IdInfo> { // SAFETY: // - `table` has static lifetime, hence it's valid for read, // - `dev` is guaranteed to be valid while it's alive, and so is `dev.as_raw()`. - let raw_id = unsafe { bindings::of_match_device(table.as_ptr(), dev.as_raw()) }; + let raw_id = + unsafe { bindings::of_match_device(table.as_raw_id_table(), dev.as_raw()) }; if !raw_id.is_null() { // SAFETY: `DeviceId` is a `#[repr(transparent)]` wrapper of `struct of_device_id` @@ -404,7 +406,7 @@ fn of_id_info(dev: &device::Device) -> Option<&'static Self::IdInfo> { // - `adev` is a valid pointer to `acpi_device` or is null. It is guaranteed to be // valid as long as `dev` is alive. // - `table` has static lifetime, hence it's valid for read. - if unsafe { acpi_of_match_device(adev, table.as_ptr(), &raw mut raw_id) } { + if unsafe { acpi_of_match_device(adev, table.as_raw_id_table(), &raw mut raw_id) } { // SAFETY: // - the function returns true, therefore `raw_id` has been set to a pointer to a // valid `of_device_id`. diff --git a/rust/kernel/i2c.rs b/rust/kernel/i2c.rs index 624b971ca8b0..920794d4089d 100644 --- a/rust/kernel/i2c.rs +++ b/rust/kernel/i2c.rs @@ -116,17 +116,17 @@ unsafe fn register( ); let i2c_table = match T::I2C_ID_TABLE { - Some(table) => table.as_ptr(), + Some(table) => table.as_raw_id_table(), None => core::ptr::null(), }; let of_table = match T::OF_ID_TABLE { - Some(table) => table.as_ptr(), + Some(table) => table.as_raw_id_table(), None => core::ptr::null(), }; let acpi_table = match T::ACPI_ID_TABLE { - Some(table) => table.as_ptr(), + Some(table) => table.as_raw_id_table(), None => core::ptr::null(), }; @@ -208,7 +208,7 @@ fn i2c_id_info(dev: &I2cClient) -> Option<&'static <Self as driver::Adapter>::Id // SAFETY: // - `table` has static lifetime, hence it's valid for reads // - `dev` is guaranteed to be valid while it's alive, and so is `dev.as_raw()`. - let raw_id = unsafe { bindings::i2c_match_id(table.as_ptr(), dev.as_raw()) }; + let raw_id = unsafe { bindings::i2c_match_id(table.as_raw_id_table(), dev.as_raw()) }; if raw_id.is_null() { return None; diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs index 5071cae6543f..311b4716800b 100644 --- a/rust/kernel/pci.rs +++ b/rust/kernel/pci.rs @@ -81,7 +81,7 @@ unsafe fn register( (*pdrv.get()).name = name.as_char_ptr(); (*pdrv.get()).probe = Some(Self::probe_callback); (*pdrv.get()).remove = Some(Self::remove_callback); - (*pdrv.get()).id_table = T::ID_TABLE.as_ptr(); + (*pdrv.get()).id_table = T::ID_TABLE.as_raw_id_table(); } // SAFETY: `pdrv` is guaranteed to be a valid `DriverType`. diff --git a/rust/kernel/platform.rs b/rust/kernel/platform.rs index 9b362e0495d3..f6a48f7750da 100644 --- a/rust/kernel/platform.rs +++ b/rust/kernel/platform.rs @@ -63,12 +63,12 @@ unsafe fn register( module: &'static ThisModule, ) -> Result { let of_table = match T::OF_ID_TABLE { - Some(table) => table.as_ptr(), + Some(table) => table.as_raw_id_table(), None => core::ptr::null(), }; let acpi_table = match T::ACPI_ID_TABLE { - Some(table) => table.as_ptr(), + Some(table) => table.as_raw_id_table(), None => core::ptr::null(), }; diff --git a/rust/kernel/usb.rs b/rust/kernel/usb.rs index 7aff0c82d0af..14e0602c3f03 100644 --- a/rust/kernel/usb.rs +++ b/rust/kernel/usb.rs @@ -58,7 +58,7 @@ unsafe fn register( (*udrv.get()).name = name.as_char_ptr(); (*udrv.get()).probe = Some(Self::probe_callback); (*udrv.get()).disconnect = Some(Self::disconnect_callback); - (*udrv.get()).id_table = T::ID_TABLE.as_ptr(); + (*udrv.get()).id_table = T::ID_TABLE.as_raw_id_table(); } // SAFETY: `udrv` is guaranteed to be a valid `DriverType`. --- base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482 change-id: 20260702-idtable-rename-asptr-3ea4d9e38287 Best regards, -- Alice Ryhl <aliceryhl(a)google.com>

1 month, 2 weeks

[PATCH] dma_buf: change unsigned int and int types into size_t

by Shahyan Soltani

The num_fences, count, i, and j variables in dma_fence_dedup_array() and __dma_fence_unwrap_merge() have inconsistent integer types, mixing both unsigned int and int. Use type size_t consistently for these instead, and update the return type of dma_fence_dedup_array() accordingly. Signed-off-by: Shahyan Soltani <shahyan.soltani(a)amd.com> Suggested-by: Philipp Stanner <phasta(a)mailbox.org> --- The rest of the subsystems (dma_resv_reserve_fences, drm_exec, drm_gpuvm, xe, nouveau, etc) uses "unsigned int" for num_fences, for example the amdgpu caller in amdgpu_userq_fence.c. drivers/dma-buf/dma-fence-unwrap.c | 8 ++++---- include/linux/dma-fence-unwrap.h | 6 ++++-- 2 files changed, 8 insertions(+), 6 deletions(-) diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c index 53bb40e70b27..65e87d263c3a 100644 --- a/drivers/dma-buf/dma-fence-unwrap.c +++ b/drivers/dma-buf/dma-fence-unwrap.c @@ -93,9 +93,9 @@ static int fence_cmp(const void *_a, const void *_b) * * Return: Number of unique fences remaining in the array. */ -int dma_fence_dedup_array(struct dma_fence **fences, int num_fences) +size_t dma_fence_dedup_array(struct dma_fence **fences, size_t num_fences) { - int i, j; + size_t i, j; sort(fences, num_fences, sizeof(*fences), fence_cmp, NULL); @@ -115,14 +115,14 @@ int dma_fence_dedup_array(struct dma_fence **fences, int num_fences) EXPORT_SYMBOL_GPL(dma_fence_dedup_array); /* Implementation for the dma_fence_merge() marco, don't use directly */ -struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences, +struct dma_fence *__dma_fence_unwrap_merge(size_t num_fences, struct dma_fence **fences, struct dma_fence_unwrap *iter) { struct dma_fence *tmp, *unsignaled = NULL, **array; struct dma_fence_array *result; ktime_t timestamp; - int i, count; + size_t i, count; count = 0; timestamp = ns_to_ktime(0); diff --git a/include/linux/dma-fence-unwrap.h b/include/linux/dma-fence-unwrap.h index 62df222fe0f1..7bfacdf79de2 100644 --- a/include/linux/dma-fence-unwrap.h +++ b/include/linux/dma-fence-unwrap.h @@ -8,6 +8,8 @@ #ifndef __LINUX_DMA_FENCE_UNWRAP_H #define __LINUX_DMA_FENCE_UNWRAP_H +#include <linux/types.h> + struct dma_fence; /** @@ -48,11 +50,11 @@ struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor); for (fence = dma_fence_unwrap_first(head, cursor); fence; \ fence = dma_fence_unwrap_next(cursor)) -struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences, +struct dma_fence *__dma_fence_unwrap_merge(size_t num_fences, struct dma_fence **fences, struct dma_fence_unwrap *cursors); -int dma_fence_dedup_array(struct dma_fence **array, int num_fences); +size_t dma_fence_dedup_array(struct dma_fence **array, size_t num_fences); /** * dma_fence_unwrap_merge - unwrap and merge fences -- 2.54.0

1 month, 2 weeks

dma_fence cleanup/rework

by Christian König

In a recent discussion with Philip and Danilo the question came up what was already tried and never finished to cleanup the dma_fence framework. So here are the different ideas I came with but never fully finished, with the patches itself modernized and rebased on top of drm-misc-next. The main goal of those changes is to make it easier to implement dma_fence backends and don't enforce unnecessary constrains on implementations. As first step the locking around the dma_fence_ops.signaled callback is made consistent by removing the dma_fence_is_signaled_locked() function. This was mostly used by backends itself, but if polling the HW is desired the backends can call their own functions for this directly without going through the dma-fence layer. XE actually seems to be the only driver which make use of that for a bit more handling. For all other cases testing the signaled flag should be enough. Then forcefully calling dma_fence_signaled() is removed from the dma-fence layer and moved into the backend implementations. This allows the backend implementations to cleanup after they have signaled the fence. Such cleanup can include removing now signaled fences from lists, dropping references, starting work etc.... Especially nouveau seems to have some really messy workaround because of that involving the DMA_FENCE_FLAG_USER_BITS and installing callbacks because the reference to the context couldn't be dropped directly after signaling. This can now be cleaned up as far as I can see. In the long term this should also allow reworking the error handling, e.g. removing dma_fence_set_error() and instead giving the error as mandatory parameter to dma_fence_signal(). Then the last piece is dropping calling enable_signaling callback with the dma_fence lock held. This makes it possible for backends to acquire locks which are semantically ordered outside of the dma_fence lock. This is necessary to allows using the dma_fence inline lock in more cases, previously backends used some common external lock for their dma_fences to for example make it possible remove fences from linked lists. Please comment and review, Christian.

1 month, 2 weeks

[PATCH v2] drm/sched: Protect entity->last_scheduled with spinlock

by Philipp Stanner

The entity->last_scheduled field has always been set and read with special RCU functions in addition to memory barriers. There is no obvious reason for that, since the entity lock is available and taken at all places that evaluate the last_scheduled field. The only exception is drm_sched_entity_error(), which is not performance critical in any way. Improve robustness, readability and maintainability by replacing RCU and barriers with the lock. As a preparational step, while at it, also guard spsc_queue_pop() with the lock, since spsc_queue is deprecated and supposed to be replaced with a locked list. Signed-off-by: Philipp Stanner <phasta(a)kernel.org> --- Changes since v1: - Add a helper variable to drop the last_scheduled reference without the entity lock being held; just to be more robust. - Write additional comment to detail the WRITE_ONCE(). --- drivers/gpu/drm/scheduler/sched_entity.c | 58 +++++++++++++----------- include/drm/gpu_scheduler.h | 9 ++-- 2 files changed, 35 insertions(+), 32 deletions(-) diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c index c51101ec70c1..12fd695c6d46 100644 --- a/drivers/gpu/drm/scheduler/sched_entity.c +++ b/drivers/gpu/drm/scheduler/sched_entity.c @@ -135,7 +135,6 @@ int drm_sched_entity_init(struct drm_sched_entity *entity, entity->num_sched_list = num_sched_list; entity->sched_list = num_sched_list > 1 ? sched_list : NULL; entity->rq = &sched_list[0]->rq; - RCU_INIT_POINTER(entity->last_scheduled, NULL); RB_CLEAR_NODE(&entity->rb_tree_node); init_completion(&entity->entity_idle); @@ -201,10 +200,10 @@ int drm_sched_entity_error(struct drm_sched_entity *entity) struct dma_fence *fence; int r; - rcu_read_lock(); - fence = rcu_dereference(entity->last_scheduled); + spin_lock(&entity->lock); + fence = entity->last_scheduled; r = fence ? fence->error : 0; - rcu_read_unlock(); + spin_unlock(&entity->lock); return r; } @@ -288,8 +287,10 @@ void drm_sched_entity_kill(struct drm_sched_entity *entity) wait_for_completion(&entity->entity_idle); /* The entity is guaranteed to not be used by the scheduler */ - prev = rcu_dereference_check(entity->last_scheduled, true); + spin_lock(&entity->lock); + prev = entity->last_scheduled; dma_fence_get(prev); + spin_unlock(&entity->lock); while ((job = drm_sched_entity_queue_pop(entity))) { struct drm_sched_fence *s_fence = job->s_fence; @@ -381,8 +382,12 @@ void drm_sched_entity_fini(struct drm_sched_entity *entity) entity->dependency = NULL; } - dma_fence_put(rcu_dereference_check(entity->last_scheduled, true)); - RCU_INIT_POINTER(entity->last_scheduled, NULL); + dma_fence_put(entity->last_scheduled); + /* + * Normally all users should be gone now, but since drm_sched has + * experienced many layering violations in the past, better be safe. + */ + WRITE_ONCE(entity->last_scheduled, NULL); drm_sched_entity_stats_put(entity->stats); } EXPORT_SYMBOL(drm_sched_entity_fini); @@ -507,6 +512,10 @@ drm_sched_job_dependency(struct drm_sched_job *job, struct drm_sched_job *drm_sched_entity_pop_job(struct drm_sched_entity *entity) { + /* Helper to avoid dropping the reference while the entity lock is held, + * just to have some more robustness. + */ + struct dma_fence *prev_last_scheduled; struct drm_sched_job *sched_job; sched_job = drm_sched_entity_queue_peek(entity); @@ -523,19 +532,20 @@ struct drm_sched_job *drm_sched_entity_pop_job(struct drm_sched_entity *entity) if (entity->guilty && atomic_read(entity->guilty)) dma_fence_set_error(&sched_job->s_fence->finished, -ECANCELED); - dma_fence_put(rcu_dereference_check(entity->last_scheduled, true)); - rcu_assign_pointer(entity->last_scheduled, - dma_fence_get(&sched_job->s_fence->finished)); + spin_lock(&entity->lock); + prev_last_scheduled = entity->last_scheduled; + entity->last_scheduled = dma_fence_get(&sched_job->s_fence->finished); - /* - * If the queue is empty we allow drm_sched_entity_select_rq() to - * locklessly access ->last_scheduled. This only works if we set the - * pointer before we dequeue and if we a write barrier here. + /* A recent rework required taking the spinlock above. Since spsc_queue + * is scheduled for removal as per the DRM-TODO-list, we access it here + * locked already to prepare for that cleanup. + * + * TODO: Fully replace spsc_queue with a locked (h)list. */ - smp_wmb(); - spsc_queue_pop(&entity->job_queue); + spin_unlock(&entity->lock); + dma_fence_put(prev_last_scheduled); drm_sched_rq_pop_entity(entity); /* Jobs and entities might have different lifecycles. Since we're @@ -561,21 +571,15 @@ void drm_sched_entity_select_rq(struct drm_sched_entity *entity) if (spsc_queue_count(&entity->job_queue)) return; - /* - * Only when the queue is empty are we guaranteed that - * drm_sched_run_job_work() cannot change entity->last_scheduled. To - * enforce ordering we need a read barrier here. See - * drm_sched_entity_pop_job() for the other side. - */ - smp_rmb(); - - fence = rcu_dereference_check(entity->last_scheduled, true); + spin_lock(&entity->lock); + fence = entity->last_scheduled; /* stay on the same engine if the previous job hasn't finished */ - if (fence && !dma_fence_is_signaled(fence)) + if (fence && !dma_fence_is_signaled(fence)) { + spin_unlock(&entity->lock); return; + } - spin_lock(&entity->lock); sched = drm_sched_pick_best(entity->sched_list, entity->num_sched_list); rq = sched ? &sched->rq : NULL; if (rq != entity->rq) { diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h index d61c19e78182..176ff1f936cd 100644 --- a/include/drm/gpu_scheduler.h +++ b/include/drm/gpu_scheduler.h @@ -100,7 +100,8 @@ struct drm_sched_entity { * @lock: * * Lock protecting the run-queue (@rq) to which this entity belongs, - * @priority and the list of schedulers (@sched_list, @num_sched_list). + * @priority, @last_scheduled and the list of schedulers (@sched_list, + * @num_sched_list). */ spinlock_t lock; @@ -202,11 +203,9 @@ struct drm_sched_entity { /** * @last_scheduled: * - * Points to the finished fence of the last scheduled job. Only written - * by drm_sched_entity_pop_job(). Can be accessed locklessly from - * drm_sched_job_arm() if the queue is empty. + * Points to the finished fence of the last scheduled job. */ - struct dma_fence __rcu *last_scheduled; + struct dma_fence *last_scheduled; /** * @last_user: last group leader pushing a job into the entity. -- 2.54.0

1 month, 2 weeks

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