Linaro-mm-sig March 2026

linaro-mm-sig@lists.linaro.org

133 participants
1109 discussions

[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

6 days, 1 hour

Re: [PATCH] drm: docs: Remove item from TODO list

by Maxime Ripard

Hi, On Mon, Oct 23, 2023 at 10:25:50AM -0700, Doug Anderson wrote: > On Mon, Oct 23, 2023 at 9:31 AM Yuran Pereira <yuran.pereira(a)hotmail.com> wrote: > > > > Since "Clean up checks for already prepared/enabled in panels" has > > already been done and merged [1], I think there is no longer a need > > for this item to be in the gpu TODO. > > > > [1] https://patchwork.freedesktop.org/patch/551421/ > > > > Signed-off-by: Yuran Pereira <yuran.pereira(a)hotmail.com> > > --- > > Documentation/gpu/todo.rst | 25 ------------------------- > > 1 file changed, 25 deletions(-) > > It's not actually all done. It's in a bit of a limbo state right now, > unfortunately. I landed all of the "simple" cases where panels were > needlessly tracking prepare/enable, but the less simple cases are > still outstanding. > > Specifically the issue is that many panels have code to properly power > cycle themselves off at shutdown time and in order to do that they > need to keep track of the prepare/enable state. After a big, long > discussion [1] it was decided that we could get rid of all the panel > code handling shutdown if only all relevant DRM KMS drivers would > properly call drm_atomic_helper_shutdown(). > > I made an attempt to get DRM KMS drivers to call > drm_atomic_helper_shutdown() [2] [3] [4]. I was able to land the > patches that went through drm-misc, but currently many of the > non-drm-misc ones are blocked waiting for attention. > > ...so things that could be done to help out: > > a) Could review patches that haven't landed in [4]. Maybe adding a > Reviewed-by tag would help wake up maintainers? > > b) Could see if you can identify panels that are exclusively used w/ > DRM drivers that have already been converted and then we could post > patches for just those panels. I have no idea how easy this task would > be. Is it enough to look at upstream dts files by "compatible" string? I think it is, yes. Maxime

1 week, 2 days

Shred Some Slopes: Getting the Hang of Snow Rider 3D

by careful.earthworm.usil＠hidingmail.com

Feeling the need for speed and a bit of winter fun, even when the weather outside is frightful? Then maybe it’s time to check out Snow Rider 3D. This simple but surprisingly addictive game offers a thrill of downhill skiing and snowboarding right from your browser, no downloads required. Let’s break down how to jump in and start enjoying this surprisingly engaging title. https://snowriderfree.com/ Gameplay: Simple Controls, Endless Possibilities The core gameplay of Snow Rider 3D is deceptively straightforward. You control your character's direction using the left and right arrow keys (or A and D). Your objective? Navigate through a series of procedurally generated slopes littered with obstacles. These obstacles range from simple ramps and rails to more challenging hazards like trees, snowdrifts, and even abandoned shacks. The beauty of Snow Rider 3D lies in its physics. While simple, they feel surprisingly realistic. You'll need to anticipate turns, adjust your speed, and time your jumps to successfully navigate the terrain. A crash will reset you to the beginning of the course, so precision and patience are key. The game offers different levels, each presenting a unique challenge. Some focus on speed and long jumps, while others demand skillful maneuvering through tight spaces. As you progress, you unlock new skins and sleds, adding a touch of customization to your experience. Think of it as a casual time-killer that can quickly turn into an hour-long obsession! Tips for Mastering the Mountain: Alright, so you're ready to hit the slopes. Here are a few tips to help you improve your runs and avoid those frustrating wipeouts: Practice Makes Perfect: Don't get discouraged by early crashes. The more you play, the better you'll understand the physics and learn to anticipate the terrain. Master the Turns: Smooth, controlled turns are essential for maintaining speed and avoiding obstacles. Practice feathering the arrow keys to make subtle adjustments. Timing is Everything: When approaching jumps and ramps, pay close attention to your speed and angle. A well-timed jump can make all the difference. Don't Be Afraid to Slow Down: Sometimes, the fastest route isn't the safest. Don't be afraid to ease off the gas and navigate tricky sections with caution. Consider looking up guides for specific levels of Snow Rider 3D at websites like Snow Rider 3D if you’re really struggling. Experiment with Sleds and Skins: Different sleds may offer slight variations in handling. Try out different options to find one that suits your playstyle. Conclusion: A Fun and Accessible Winter Escape Snow Rider 3D is a surprisingly addictive and accessible game that’s perfect for a quick dose of winter fun. It's simple controls and challenging gameplay make it easy to pick up and play, while its procedural generation ensures that each run is a unique experience. So, whether you're looking for a casual time-killer or a challenging skill-based game, Snow Rider 3D is definitely worth checking out.

1 week, 6 days

Why should you buy a dachshund puppy?

by Chong Criston

2 weeks, 5 days

[PATCH 0/5] Replace the dmabuf custom test framework with kunit

by Jason Gunthorpe

Using kunit to write tests for new work on dmabuf is coming up: https://lore.kernel.org/all/26-v1-b5cab63049c0+191af-dmabuf_map_type_jgg@nv… Replace the custom test framework with kunit to avoid maintaining two concurrent test frameworks. The conversion minimizes code changes and uses simple pattern-oriented reworks to reduce the chance of breaking any tests. Aside from adding the kunit_test_suite() boilerplate, the conversion follows a number of patterns: Test failures without cleanup. For example: if (!ptr) return -ENOMEM; Becomes: KUNIT_ASSERT_NOT_NULL(test, ptr); In kunit ASSERT longjumps out of the test. Check for error, fail and cleanup: if (err) { pr_err("msg\n"); goto cleanup; } Becomes: if (err) { KUNIT_FAIL(test, "msg"); goto cleanup; } Preserve the existing failure messages and cleanup code. Cases where the test returns err but prints no message: if (err) goto cleanup; Becomes: if (err) { KUNIT_FAIL(test, "msg"); goto cleanup; } Use KUNIT_FAIL to retain the 'cleanup on err' behavior. Overall, the conversion is straightforward. The result can be run with kunit.py: $ tools/testing/kunit/kunit.py run --build_dir build_kunit_x86_64 --arch x86_64 --kunitconfig ./drivers/dma-buf/.kunitconfig [20:37:23] Configuring KUnit Kernel ... [20:37:23] Building KUnit Kernel ... Populating config with: $ make ARCH=x86_64 O=build_kunit_x86_64 olddefconfig Building with: $ make all compile_commands.json scripts_gdb ARCH=x86_64 O=build_kunit_x86_64 --jobs=20 [20:37:29] Starting KUnit Kernel (1/1)... [20:37:29] ============================================================ Running tests with: $ qemu-system-x86_64 -nodefaults -m 1024 -kernel build_kunit_x86_64/arch/x86/boot/bzImage -append 'kunit.enable=1 console=ttyS0 kunit_shutdown=reboot' -no-reboot -nographic -accel kvm -accel hvf -accel tcg -serial stdio -bios qboot.rom [20:37:30] ================ dma-buf-resv (5 subtests) ================= [20:37:30] [PASSED] test_sanitycheck [20:37:30] ===================== test_signaling ====================== [20:37:30] [PASSED] kernel [20:37:30] [PASSED] write [20:37:30] [PASSED] read [20:37:30] [PASSED] bookkeep [20:37:30] ================= [PASSED] test_signaling ================== ... [20:37:35] Testing complete. Ran 50 tests: passed: 49, skipped: 1 [20:37:35] Elapsed time: 12.635s total, 0.001s configuring, 6.551s building, 6.017s running One test that requires two CPUs is skipped since the default VM has a single CPU and cannot run the test. All other usual ways to run kunit work as well, and all tests are placed in a module to provide more options for how they are run. AI was used to do the large scale semantic search and replaces described above, then everything was hand checked. AI also deduced the issue with test_race_signal_callback() in a couple of seconds from the kunit crash (!!), again was hand checked though I am not so familiar with this test to be fully certain this is the best answer. Jason Gunthorpe (5): dma-buf: Change st-dma-resv.c to use kunit dma-buf: Change st-dma-fence.c to use kunit dma-buf: Change st-dma-fence-unwrap.c to use kunit dma-buf: Change st-dma-fence-chain.c to use kunit dma-buf: Remove the old selftest drivers/dma-buf/.kunitconfig | 2 + drivers/dma-buf/Kconfig | 11 +- drivers/dma-buf/Makefile | 5 +- drivers/dma-buf/selftest.c | 167 --------------- drivers/dma-buf/selftest.h | 30 --- drivers/dma-buf/selftests.h | 16 -- drivers/dma-buf/st-dma-fence-chain.c | 217 +++++++++---------- drivers/dma-buf/st-dma-fence-unwrap.c | 290 +++++++++++--------------- drivers/dma-buf/st-dma-fence.c | 200 ++++++++---------- drivers/dma-buf/st-dma-resv.c | 145 +++++++------ drivers/gpu/drm/i915/Kconfig.debug | 2 +- 11 files changed, 394 insertions(+), 691 deletions(-) create mode 100644 drivers/dma-buf/.kunitconfig delete mode 100644 drivers/dma-buf/selftest.c delete mode 100644 drivers/dma-buf/selftest.h delete mode 100644 drivers/dma-buf/selftests.h base-commit: 41dae5ac5e157b0bb260f381eb3df2f4a4610205 -- 2.43.0

3 weeks, 1 day

[PATCH v5 0/2] dma-buf: heaps: system: add an option to allocate explicitly shared/decrypted memory

by Jiri Pirko

From: Jiri Pirko <jiri(a)nvidia.com> Confidential computing (CoCo) VMs/guests, such as AMD SEV and Intel TDX, run with private/encrypted memory which creates a challenge for devices that do not support DMA to it (no TDISP support). For kernel-only DMA operations, swiotlb bounce buffering provides a transparent solution by copying data through shared memory. However, the only way to get this memory into userspace is via the DMA API's dma_alloc_pages()/dma_mmap_pages() type interfaces which limits the use of the memory to a single DMA device, and is incompatible with pin_user_pages(). These limitations are particularly problematic for the RDMA subsystem which makes heavy use of pin_user_pages() and expects flexible memory usage between many different DMA devices. This patch series enables userspace to explicitly request shared (decrypted) memory allocations from new dma-buf system_cc_shared heap. Userspace can mmap this memory and pass the dma-buf fd to other existing importers such as RDMA or DRM devices to access the memory. The DMA API is improved to allow the dma heap exporter to DMA map the shared memory to each importing device. Based on dma-mapping-for-next e7442a68cd1ee797b585f045d348781e9c0dde0d Jiri Pirko (2): dma-mapping: introduce DMA_ATTR_CC_SHARED for shared memory dma-buf: heaps: system: add system_cc_shared heap for explicitly shared memory drivers/dma-buf/heaps/system_heap.c | 103 ++++++++++++++++++++++++++-- include/linux/dma-mapping.h | 10 +++ include/trace/events/dma.h | 3 +- kernel/dma/direct.h | 14 +++- kernel/dma/mapping.c | 13 +++- 5 files changed, 132 insertions(+), 11 deletions(-) -- 2.51.1

1 month, 2 weeks

[PATCH 00/13] Add DMA support for LINFlexD UART driver

by Larisa Grigore

This patchset enhances the LINFlexD UART driver and its device tree bindings to support DMA transfers, configurable clock inputs, dynamic baudrate changes, and termios features. It also includes a series of fixes and improvements to ensure reliable operation across various modes and configurations. The changes added can be summarized as follows: 1. Fixes with respect to FIFO handling, locking, interrupt related registers and INITM mode transition. 2. Removal of the earlycon workaround, as proper FIFO handling and INITM transitions now ensure stable behavior. 3. Support for configurable stop bits and dynamic baudrate changes based on clock inputs and termios settings. 4. Optional DMA support for RX and TX paths, preventing character loss during high-throughput operations like copy-paste. Cyclic DMA is used for RX to avoid gaps between transactions. Larisa Grigore (8): serial: linflexuart: Clean SLEEP bit in LINCR1 after suspend serial: linflexuart: Check FIFO full before writing serial: linflexuart: Correctly clear UARTSR in buffer mode serial: linflexuart: Update RXEN/TXEN outside INITM mode serial: linflexuart: Ensure FIFO is empty when entering INITM serial: linflexuart: Revert earlycon workaround serial: linflexuart: Add support for configurable stop bits serial: linflexuart: Add DMA support Radu Pirea (5): serial: linflexuart: Fix locking in set_termios dt-bindings: serial: fsl-linflexuart: add clock input properties dt-bindings: serial: fsl-linflexuart: add dma properties serial: linflexuart: Add support for changing baudrate serial: linflexuart: Avoid stopping DMA during receive operations .../bindings/serial/fsl,s32-linflexuart.yaml | 31 + drivers/tty/serial/fsl_linflexuart.c | 972 +++++++++++++++--- 2 files changed, 846 insertions(+), 157 deletions(-) -- 2.47.0

1 month, 3 weeks

[PATCH v2 00/10] dma-bug: heaps: Add Tegra VPR support

by Thierry Reding

From: Thierry Reding <treding(a)nvidia.com> Hi, This series adds support for the video protection region (VPR) used on Tegra SoC devices. It's a special region of memory that is protected from accesses by the CPU and used to store DRM protected content (both decrypted stream data as well as decoded video frames). Patches 1 and 2 add DT binding documentation for the VPR and add the VPR to the list of memory-region items for display and host1x. Patch 3 adds bitmap_allocate(), which is like bitmap_allocate_region() but works on sizes that are not a power of two. Patch 4 introduces new APIs needed by the Tegra VPR implementation that allow CMA areas to be dynamically created at runtime rather than using the fixed, system-wide list. This is used in this driver specifically because it can use an arbitrary number of these areas (though they are currently limited to 4). Patch 5 adds some infrastructure for DMA heap implementations to provide information through debugfs. The Tegra VPR implementation is added in patch 6. See its commit message for more details about the specifics of this implementation. Finally, patches 7-10 add the VPR placeholder node on Tegra234 and hook it up to the host1x and GPU nodes so that they can make use of this region. Changes in v2: - Tegra VPR implementation is now more optimized to reduce the number of (very slow) resize operations, and allows cross-chunk allocations - dynamic CMA areas are now trackd separately from static ones, but the global number of CMA pages accounts for all areas Thierry Thierry Reding (10): dt-bindings: reserved-memory: Document Tegra VPR dt-bindings: display: tegra: Document memory regions bitmap: Add bitmap_allocate() function mm/cma: Allow dynamically creating CMA areas dma-buf: heaps: Add debugfs support dma-buf: heaps: Add support for Tegra VPR arm64: tegra: Add VPR placeholder node on Tegra234 arm64: tegra: Add GPU node on Tegra234 arm64: tegra: Hook up VPR to host1x arm64: tegra: Hook up VPR to the GPU .../display/tegra/nvidia,tegra186-dc.yaml | 10 + .../display/tegra/nvidia,tegra20-dc.yaml | 10 +- .../display/tegra/nvidia,tegra20-host1x.yaml | 7 + .../nvidia,tegra-video-protection-region.yaml | 55 + arch/arm/mm/dma-mapping.c | 2 +- arch/arm64/boot/dts/nvidia/tegra234.dtsi | 60 + arch/s390/mm/init.c | 2 +- drivers/dma-buf/dma-heap.c | 56 + drivers/dma-buf/heaps/Kconfig | 7 + drivers/dma-buf/heaps/Makefile | 1 + drivers/dma-buf/heaps/cma_heap.c | 2 +- drivers/dma-buf/heaps/tegra-vpr.c | 1265 +++++++++++++++++ include/linux/bitmap.h | 25 +- include/linux/cma.h | 7 +- include/linux/dma-heap.h | 2 + include/trace/events/tegra_vpr.h | 57 + mm/cma.c | 187 ++- mm/cma.h | 5 +- 18 files changed, 1713 insertions(+), 47 deletions(-) create mode 100644 Documentation/devicetree/bindings/reserved-memory/nvidia,tegra-video-protection-region.yaml create mode 100644 drivers/dma-buf/heaps/tegra-vpr.c create mode 100644 include/trace/events/tegra_vpr.h -- 2.52.0

2 months

[PATCH v2] dma-buf/udmabuf: skip redundant cpu sync to fix cacheline EEXIST warning

by Mikhail Gavrilov

When CONFIG_DMA_API_DEBUG_SG is enabled, importing a udmabuf into a DRM driver (e.g. amdgpu for video playback in GNOME Videos / Showtime) triggers a spurious warning: DMA-API: amdgpu 0000:03:00.0: cacheline tracking EEXIST, \ overlapping mappings aren't supported WARNING: kernel/dma/debug.c:619 at add_dma_entry+0x473/0x5f0 The call chain is: amdgpu_cs_ioctl -> amdgpu_ttm_backend_bind -> dma_buf_map_attachment -> [udmabuf] map_udmabuf -> get_sg_table -> dma_map_sgtable(dev, sg, direction, 0) // attrs=0 -> debug_dma_map_sg -> add_dma_entry -> EEXIST This happens because udmabuf builds a per-page scatter-gather list via sg_set_folio(). When begin_cpu_udmabuf() has already created an sg table mapped for the misc device, and an importer such as amdgpu maps the same pages for its own device via map_udmabuf(), the DMA debug infrastructure sees two active mappings whose physical addresses share cacheline boundaries and warns about the overlap. The DMA_ATTR_SKIP_CPU_SYNC flag suppresses this check in add_dma_entry() because it signals that no CPU cache maintenance is performed at map/unmap time, making the cacheline overlap harmless. All other major dma-buf exporters already pass this flag: - drm_gem_map_dma_buf() passes DMA_ATTR_SKIP_CPU_SYNC - amdgpu_dma_buf_map() passes DMA_ATTR_SKIP_CPU_SYNC The CPU sync at map/unmap time is also redundant for udmabuf: begin_cpu_udmabuf() and end_cpu_udmabuf() already perform explicit cache synchronization via dma_sync_sgtable_for_cpu/device() when CPU access is requested through the dma-buf interface. Pass DMA_ATTR_SKIP_CPU_SYNC to dma_map_sgtable() and dma_unmap_sgtable() in udmabuf to suppress the spurious warning and skip the redundant sync. Fixes: 284562e1f348 ("udmabuf: implement begin_cpu_access/end_cpu_access hooks") Cc: stable(a)vger.kernel.org Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov(a)gmail.com> --- v1 -> v2: - Rebased on drm-tip to resolve conflict with folio conversion patches. No code change, same two-line fix. v1: https://lore.kernel.org/all/20260317053653.28888-1-mikhail.v.gavrilov@gmail… drivers/dma-buf/udmabuf.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c index 94b26ea706a3..bced421c0d65 100644 --- a/drivers/dma-buf/udmabuf.c +++ b/drivers/dma-buf/udmabuf.c @@ -145,7 +145,7 @@ static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf, if (ret < 0) goto err_alloc; - ret = dma_map_sgtable(dev, sg, direction, 0); + ret = dma_map_sgtable(dev, sg, direction, DMA_ATTR_SKIP_CPU_SYNC); if (ret < 0) goto err_map; return sg; @@ -160,7 +160,7 @@ static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf, static void put_sg_table(struct device *dev, struct sg_table *sg, enum dma_data_direction direction) { - dma_unmap_sgtable(dev, sg, direction, 0); + dma_unmap_sgtable(dev, sg, direction, DMA_ATTR_SKIP_CPU_SYNC); sg_free_table(sg); kfree(sg); } -- 2.53.0

2 months, 1 week

[PATCH RFC 00/26] Add DMA-buf mapping types and convert vfio/iommufd to use them

by Jason Gunthorpe

Since its introduction, DMA-buf has only supported using scatterlist for the exporter and importer to exchange address information. This is not sufficient for all use cases as dma_addr_t is a very specific and limited type that should not be abused for things unrelated to the DMA API. There are several motivations for addressing this now: 1) VFIO to IOMMUFD and KVM requires a physical address, not a dma_addr_t scatterlist, it cannot be represented in the scatterlist structure 2) xe vGPU requires the host driver to accept a DMABUF from VFIO of its own VF and convert it into an internal VRAM address on the PF 3) We are starting to look at replacement datastructures for scatterlist 4) Ideas around UALink/etc are suggesting not using the DMA API None of these can sanely be achieved using scatterlist. Introduce a new mechanism called "mapping types" which allows DMA-buf to work with more map/unmap options than scatterlist. Each mapping type encompasses a full set of functions and data unique to itself. The core code provides a match-making system to select the best type offered by the exporter and importer to be the active mapping type for the attachment. Everything related to scatterlist is moved into a DMA-buf SGT mapping type, and into the "dma_buf_sgt_*" namespace for clarity. Existing exporters are moved over to explicitly declare SGT mapping types and importers are adjusted to use the dma_buf_sgt_* named importer helpers. Mapping types are designed to be extendable, a driver can declare its own mapping type for its internal private interconnect and use that without having to adjust the core code. The new attachment sequence starts with the importing driver declaring what mapping types it can accept: struct dma_buf_mapping_match imp_match[] = { DMA_BUF_IMAPPING_MY_DRIVER(dev, ...), DMA_BUF_IMAPPING_SGT(dev, false), }; attach = dma_buf_mapping_attach(dmabuf, imp_match, ...) Most drivers will do this via a dma_buf_sgt_*attach() helper. The exporting driver can then declare what mapping types it can supply: int exporter_match_mapping(struct dma_buf_match_args *args) { struct dma_buf_mapping_match exp_match[] = { DMA_BUF_EMAPPING_MY_DRIVER(my_ops, dev, ...), DMA_BUF_EMAPPING_SGT(sgt_ops, dev, false), DMA_BUF_EMAPPING_PAL(PAL_ops), }; return dma_buf_match_mapping(args, exp_match, ...); } Most drivers will do this via a helper: static const struct dma_buf_ops ops = { DMA_BUF_SIMPLE_SGT_EXP_MATCH(map_func, unmap_func) }; During dma_buf_mapping_attach() the core code will select a mutual match between the importer and exporter and record it as the active match in the attach->map_type. Each mapping type has its own types/function calls for mapping/unmapping, and storage in the attach->map_type for its information. As such each mapping type can offer function signatures and data that exactly matches its needs. This series goes through a sequence of: 1) Introduce the basic mapping type framework and the main components of the SGT mapping type 2) Automatically make all existing exporters and importers use core generated SGT mapping types so every attachment has a SGT mapping type 3) Convert all exporter drivers to natively create a SGT mapping type 4) Move all dma_buf_* functions and types that are related to SGT into dma_buf_sgt_* 5) Remove all the now-unused items that have been moved into SGT specific structures. 6) Demonstrate adding a new Physical Address List alongside SGT. Due to the high number of files touched I would expect this to be broken into phases, but this shows the entire picture. This is on github: https://github.com/jgunthorpe/linux/commits/dmabuf_map_type It is a followup to the discussion here: https://lore.kernel.org/dri-devel/20251027044712.1676175-1-vivek.kasireddy@… Jason Gunthorpe (26): dma-buf: Introduce DMA-buf mapping types dma-buf: Add the SGT DMA mapping type dma-buf: Add dma_buf_mapping_attach() dma-buf: Route SGT related actions through attach->map_type dma-buf: Allow single exporter drivers to avoid the match_mapping function drm: Check the SGT ops for drm_gem_map_dma_buf() dma-buf: Convert all the simple exporters to use SGT mapping type drm/vmwgfx: Use match_mapping instead of dummy calls accel/habanalabs: Use the SGT mapping type drm/xe/dma-buf: Use the SGT mapping type drm/amdgpu: Use the SGT mapping type vfio/pci: Change the DMA-buf exporter to use mapping_type dma-buf: Update dma_buf_phys_vec_to_sgt() to use the SGT mapping type iio: buffer: convert to use the SGT mapping type functionfs: convert to use the SGT mapping type dma-buf: Remove unused SGT stuff from the common structures treewide: Rename dma_buf_map_attachment(_unlocked) to dma_buf_sgt_ treewide: Rename dma_buf_unmap_attachment(_unlocked) to dma_buf_sgt_* treewide: Rename dma_buf_attach() to dma_buf_sgt_attach() treewide: Rename dma_buf_dynamic_attach() to dma_buf_sgt_dynamic_attach() dma-buf: Add the Physical Address List DMA mapping type vfio/pci: Add physical address list support to DMABUF iommufd: Use the PAL mapping type instead of a vfio function iommufd: Support DMA-bufs with multiple physical ranges iommufd/selftest: Check multi-phys DMA-buf scenarios dma-buf: Add kunit tests for mapping type Documentation/gpu/todo.rst | 2 +- drivers/accel/amdxdna/amdxdna_gem.c | 14 +- drivers/accel/amdxdna/amdxdna_ubuf.c | 10 +- drivers/accel/habanalabs/common/memory.c | 54 ++- drivers/accel/ivpu/ivpu_gem.c | 10 +- drivers/accel/ivpu/ivpu_gem_userptr.c | 11 +- drivers/accel/qaic/qaic_data.c | 8 +- drivers/dma-buf/Makefile | 1 + drivers/dma-buf/dma-buf-mapping.c | 186 ++++++++- drivers/dma-buf/dma-buf.c | 180 ++++++--- drivers/dma-buf/heaps/cma_heap.c | 12 +- drivers/dma-buf/heaps/system_heap.c | 13 +- drivers/dma-buf/st-dma-mapping.c | 373 ++++++++++++++++++ drivers/dma-buf/udmabuf.c | 8 +- drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 98 +++-- drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 6 +- drivers/gpu/drm/armada/armada_gem.c | 33 +- drivers/gpu/drm/drm_gem_shmem_helper.c | 2 +- drivers/gpu/drm/drm_prime.c | 31 +- drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 18 +- drivers/gpu/drm/i915/gem/i915_gem_object.c | 2 +- .../drm/i915/gem/selftests/i915_gem_dmabuf.c | 8 +- .../gpu/drm/i915/gem/selftests/mock_dmabuf.c | 8 +- drivers/gpu/drm/msm/msm_gem_prime.c | 7 +- drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c | 11 +- drivers/gpu/drm/tegra/gem.c | 33 +- drivers/gpu/drm/virtio/virtgpu_prime.c | 23 +- drivers/gpu/drm/vmwgfx/vmwgfx_prime.c | 32 +- drivers/gpu/drm/xe/xe_bo.c | 18 +- drivers/gpu/drm/xe/xe_dma_buf.c | 61 +-- drivers/iio/industrialio-buffer.c | 15 +- drivers/infiniband/core/umem_dmabuf.c | 15 +- drivers/iommu/iommufd/io_pagetable.h | 4 +- drivers/iommu/iommufd/iommufd_private.h | 8 - drivers/iommu/iommufd/iommufd_test.h | 7 + drivers/iommu/iommufd/pages.c | 85 ++-- drivers/iommu/iommufd/selftest.c | 177 ++++++--- .../media/common/videobuf2/videobuf2-core.c | 2 +- .../common/videobuf2/videobuf2-dma-contig.c | 26 +- .../media/common/videobuf2/videobuf2-dma-sg.c | 21 +- .../common/videobuf2/videobuf2-vmalloc.c | 13 +- .../platform/nvidia/tegra-vde/dmabuf-cache.c | 9 +- drivers/misc/fastrpc.c | 21 +- drivers/tee/tee_heap.c | 13 +- drivers/usb/gadget/function/f_fs.c | 11 +- drivers/vfio/pci/vfio_pci_dmabuf.c | 79 ++-- drivers/xen/gntdev-dmabuf.c | 29 +- include/linux/dma-buf-mapping.h | 297 ++++++++++++++ include/linux/dma-buf.h | 168 ++++---- io_uring/zcrx.c | 9 +- net/core/devmem.c | 14 +- samples/vfio-mdev/mbochs.c | 10 +- sound/soc/fsl/fsl_asrc_m2m.c | 12 +- tools/testing/selftests/iommu/iommufd.c | 43 ++ tools/testing/selftests/iommu/iommufd_utils.h | 17 + 55 files changed, 1764 insertions(+), 614 deletions(-) create mode 100644 drivers/dma-buf/st-dma-mapping.c base-commit: c63e5a50e1dd291cd95b04291b028fdcaba4c534 -- 2.43.0

2 months, 2 weeks

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