Linaro-mm-sig

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7077 discussions

[PATCH] dma-buf: check the return value of kstrdup()

by xkernel.wang＠foxmail.com

From: Xiaoke Wang <xkernel.wang(a)foxmail.com> kstrdup() is a memory allocation function which can return NULL when some internaly memory errors happen. It is better to check the return value of it to prevent further wrong memory access. Signed-off-by: Xiaoke Wang <xkernel.wang(a)foxmail.com> --- drivers/dma-buf/selftest.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/dma-buf/selftest.c b/drivers/dma-buf/selftest.c index c60b694..2c29e2a 100644 --- a/drivers/dma-buf/selftest.c +++ b/drivers/dma-buf/selftest.c @@ -50,6 +50,9 @@ static bool apply_subtest_filter(const char *caller, const char *name) bool result = true; filter = kstrdup(__st_filter, GFP_KERNEL); + if (!filter) + return false; + for (sep = filter; (tok = strsep(&sep, ","));) { bool allow = true; char *sl; --

4 years, 6 months

[PATCH] drm/amdgpu: check vm bo eviction valuable at last

by Qiang Yu

Workstation application ANSA/META get this error dmesg: [drm:amdgpu_gem_va_ioctl [amdgpu]] *ERROR* Couldn't update BO_VA (-16) This is caused by: 1. create a 256MB buffer in invisible VRAM 2. CPU map the buffer and access it causes vm_fault and try to move it to visible VRAM 3. force visible VRAM space and traverse all VRAM bos to check if evicting this bo is valuable 4. when checking a VM bo (in invisible VRAM), amdgpu_vm_evictable() will set amdgpu_vm->evicting, but latter due to not in visible VRAM, won't really evict it so not add it to amdgpu_vm->evicted 5. before next CS to clear the amdgpu_vm->evicting, user VM ops ioctl will pass amdgpu_vm_ready() (check amdgpu_vm->evicted) but fail in amdgpu_vm_bo_update_mapping() (check amdgpu_vm->evicting) and get this error log This error won't affect functionality as next CS will finish the waiting VM ops. But we'd better make the amdgpu_vm->evicting correctly reflact the vm status and clear the error log. Signed-off-by: Qiang Yu <qiang.yu(a)amd.com> --- drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 85 ++++++++++++++----------- 1 file changed, 47 insertions(+), 38 deletions(-) diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c index 5a32ee66d8c8..88a27911054f 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c @@ -1306,45 +1306,11 @@ uint64_t amdgpu_ttm_tt_pte_flags(struct amdgpu_device *adev, struct ttm_tt *ttm, return flags; } -/* - * amdgpu_ttm_bo_eviction_valuable - Check to see if we can evict a buffer - * object. - * - * Return true if eviction is sensible. Called by ttm_mem_evict_first() on - * behalf of ttm_bo_mem_force_space() which tries to evict buffer objects until - * it can find space for a new object and by ttm_bo_force_list_clean() which is - * used to clean out a memory space. - */ -static bool amdgpu_ttm_bo_eviction_valuable(struct ttm_buffer_object *bo, - const struct ttm_place *place) +static bool amdgpu_ttm_mem_eviction_valuable(struct ttm_buffer_object *bo, + const struct ttm_place *place) { unsigned long num_pages = bo->resource->num_pages; struct amdgpu_res_cursor cursor; - struct dma_resv_list *flist; - struct dma_fence *f; - int i; - - /* Swapout? */ - if (bo->resource->mem_type == TTM_PL_SYSTEM) - return true; - - if (bo->type == ttm_bo_type_kernel && - !amdgpu_vm_evictable(ttm_to_amdgpu_bo(bo))) - return false; - - /* If bo is a KFD BO, check if the bo belongs to the current process. - * If true, then return false as any KFD process needs all its BOs to - * be resident to run successfully - */ - flist = dma_resv_shared_list(bo->base.resv); - if (flist) { - for (i = 0; i < flist->shared_count; ++i) { - f = rcu_dereference_protected(flist->shared[i], - dma_resv_held(bo->base.resv)); - if (amdkfd_fence_check_mm(f, current->mm)) - return false; - } - } switch (bo->resource->mem_type) { case AMDGPU_PL_PREEMPT: @@ -1377,10 +1343,53 @@ static bool amdgpu_ttm_bo_eviction_valuable(struct ttm_buffer_object *bo, return false; default: - break; + return ttm_bo_eviction_valuable(bo, place); } +} - return ttm_bo_eviction_valuable(bo, place); +/* + * amdgpu_ttm_bo_eviction_valuable - Check to see if we can evict a buffer + * object. + * + * Return true if eviction is sensible. Called by ttm_mem_evict_first() on + * behalf of ttm_bo_mem_force_space() which tries to evict buffer objects until + * it can find space for a new object and by ttm_bo_force_list_clean() which is + * used to clean out a memory space. + */ +static bool amdgpu_ttm_bo_eviction_valuable(struct ttm_buffer_object *bo, + const struct ttm_place *place) +{ + struct dma_resv_list *flist; + struct dma_fence *f; + int i; + + /* Swapout? */ + if (bo->resource->mem_type == TTM_PL_SYSTEM) + return true; + + /* If bo is a KFD BO, check if the bo belongs to the current process. + * If true, then return false as any KFD process needs all its BOs to + * be resident to run successfully + */ + flist = dma_resv_shared_list(bo->base.resv); + if (flist) { + for (i = 0; i < flist->shared_count; ++i) { + f = rcu_dereference_protected(flist->shared[i], + dma_resv_held(bo->base.resv)); + if (amdkfd_fence_check_mm(f, current->mm)) + return false; + } + } + + /* Check by different mem type. */ + if (!amdgpu_ttm_mem_eviction_valuable(bo, place)) + return false; + + /* VM bo should be checked at last because it will mark VM evicting. */ + if (bo->type == ttm_bo_type_kernel) + return amdgpu_vm_evictable(ttm_to_amdgpu_bo(bo)); + + return true; } static void amdgpu_ttm_vram_mm_access(struct amdgpu_device *adev, loff_t pos, -- 2.25.1

4 years, 6 months

ACCOUNT WARNING: Undelivered mails linaro-mm-sig@lists.linaro.org Kindly rectify

by Noreply＠lists.linaro.org

4 years, 6 months

[RFC v2 0/6] Proposal for a GPU cgroup controller

by T.J. Mercier

This patch series revisits the proposal for a GPU cgroup controller to track and limit memory allocations by various device/allocator subsystems. The patch series also contains a simple prototype to illustrate how Android intends to implement DMA-BUF allocator attribution using the GPU cgroup controller. The prototype does not include resource limit enforcements. Changelog: v2: See the previous revision of this change submitted by Hridya Valsaraju at: https://lore.kernel.org/all/20220115010622.3185921-1-hridya@google.com/ Move dma-buf cgroup charge transfer from a dma_buf_op defined by every heap to a single dma-buf function for all heaps per Daniel Vetter and Christian König. Pointers to struct gpucg and struct gpucg_device tracking the current associations were added to the dma_buf struct to achieve this. Fix incorrect Kconfig help section indentation per Randy Dunlap. History of the GPU cgroup controller ==================================== The GPU/DRM cgroup controller came into being when a consensus[1] was reached that the resources it tracked were unsuitable to be integrated into memcg. Originally, the proposed controller was specific to the DRM subsystem and was intended to track GEM buffers and GPU-specific resources[2]. In order to help establish a unified memory accounting model for all GPU and all related subsystems, Daniel Vetter put forth a suggestion to move it out of the DRM subsystem so that it can be used by other DMA-BUF exporters as well[3]. This RFC proposes an interface that does the same. [1]: https://patchwork.kernel.org/project/dri-devel/cover/20190501140438.9506-1-… [2]: https://lore.kernel.org/amd-gfx/20210126214626.16260-1-brian.welty@intel.co… [3]: https://lore.kernel.org/amd-gfx/YCVOl8%2F87bqRSQei@phenom.ffwll.local/ T.J. Mercier (6): gpu: rfc: Proposal for a GPU cgroup controller cgroup: gpu: Add a cgroup controller for allocator attribution of GPU memory dmabuf: Use the GPU cgroup charge/uncharge APIs dmabuf: heaps: export system_heap buffers with GPU cgroup charging dmabuf: Add gpu cgroup charge transfer function android: binder: Add a buffer flag to relinquish ownership of fds Documentation/gpu/rfc/gpu-cgroup.rst | 195 +++++++++++++++++ Documentation/gpu/rfc/index.rst | 4 + drivers/android/binder.c | 26 +++ drivers/dma-buf/dma-buf.c | 100 +++++++++ drivers/dma-buf/dma-heap.c | 27 +++ drivers/dma-buf/heaps/system_heap.c | 3 + include/linux/cgroup_gpu.h | 127 +++++++++++ include/linux/cgroup_subsys.h | 4 + include/linux/dma-buf.h | 22 +- include/linux/dma-heap.h | 11 + include/uapi/linux/android/binder.h | 1 + init/Kconfig | 7 + kernel/cgroup/Makefile | 1 + kernel/cgroup/gpu.c | 304 +++++++++++++++++++++++++++ 14 files changed, 830 insertions(+), 2 deletions(-) create mode 100644 Documentation/gpu/rfc/gpu-cgroup.rst create mode 100644 include/linux/cgroup_gpu.h create mode 100644 kernel/cgroup/gpu.c -- 2.35.1.265.g69c8d7142f-goog

4 years, 6 months

completely rework the dma_resv semantic

by Christian König

Hi guys, by now that should be a rather well known set of changes. The basic idea is that instead of the fixed exclusive/shared classes we now attach an usage to each fence in the dma_resv object describing how the operation represented by the fence is using the resources protected by the dma_resv. I've addressed quite a bunch of comments already and I think this set has already been discussed quite well now. As improvement to the last version I've now added CCs for all the relevant maintainers to the patches changing some functionality inside drivers. Please review and comment, Christian.

4 years, 6 months

[PATCH] drm/i915/gt: fix unsigned integer to signed assignment

by Jiapeng Chong

Eliminate the follow smatch warning: drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c:4640 guc_create_virtual() warn: assigning (-2) to unsigned variable 've->base.instance'. drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c:4641 guc_create_virtual() warn: assigning (-2) to unsigned variable 've->base.uabi_instance'. Reported-by: Abaci Robot <abaci(a)linux.alibaba.com> Signed-off-by: Jiapeng Chong <jiapeng.chong(a)linux.alibaba.com> --- drivers/gpu/drm/i915/gt/intel_engine_types.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h index 36365bdbe1ee..dc7cc06c68e7 100644 --- a/drivers/gpu/drm/i915/gt/intel_engine_types.h +++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h @@ -328,10 +328,10 @@ struct intel_engine_cs { intel_engine_mask_t logical_mask; u8 class; - u8 instance; + s8 instance; u16 uabi_class; - u16 uabi_instance; + s16 uabi_instance; u32 uabi_capabilities; u32 context_size; -- 2.20.1.7.g153144c

4 years, 6 months

[PATCH v3] kfence: Make test case compatible with run time set sample interval

by Peng Liu

The parameter kfence_sample_interval can be set via boot parameter and late shell command, which is convenient for automated tests and KFENCE parameter optimization. However, KFENCE test case just uses compile-time CONFIG_KFENCE_SAMPLE_INTERVAL, which will make KFENCE test case not run as users desired. Export kfence_sample_interval, so that KFENCE test case can use run-time-set sample interval. Signed-off-by: Peng Liu <liupeng256(a)huawei.com> --- v2->v3: - Revise change log description v1->v2: - Use EXPORT_SYMBOL_GPL replace EXPORT_SYMBOL include/linux/kfence.h | 2 ++ mm/kfence/core.c | 3 ++- mm/kfence/kfence_test.c | 8 ++++---- 3 files changed, 8 insertions(+), 5 deletions(-) diff --git a/include/linux/kfence.h b/include/linux/kfence.h index 4b5e3679a72c..f49e64222628 100644 --- a/include/linux/kfence.h +++ b/include/linux/kfence.h @@ -17,6 +17,8 @@ #include <linux/atomic.h> #include <linux/static_key.h> +extern unsigned long kfence_sample_interval; + /* * We allocate an even number of pages, as it simplifies calculations to map * address to metadata indices; effectively, the very first page serves as an diff --git a/mm/kfence/core.c b/mm/kfence/core.c index 5ad40e3add45..13128fa13062 100644 --- a/mm/kfence/core.c +++ b/mm/kfence/core.c @@ -47,7 +47,8 @@ static bool kfence_enabled __read_mostly; -static unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE_INTERVAL; +unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE_INTERVAL; +EXPORT_SYMBOL_GPL(kfence_sample_interval); /* Export for test modules. */ #ifdef MODULE_PARAM_PREFIX #undef MODULE_PARAM_PREFIX diff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c index a22b1af85577..50dbb815a2a8 100644 --- a/mm/kfence/kfence_test.c +++ b/mm/kfence/kfence_test.c @@ -268,13 +268,13 @@ static void *test_alloc(struct kunit *test, size_t size, gfp_t gfp, enum allocat * 100x the sample interval should be more than enough to ensure we get * a KFENCE allocation eventually. */ - timeout = jiffies + msecs_to_jiffies(100 * CONFIG_KFENCE_SAMPLE_INTERVAL); + timeout = jiffies + msecs_to_jiffies(100 * kfence_sample_interval); /* * Especially for non-preemption kernels, ensure the allocation-gate * timer can catch up: after @resched_after, every failed allocation * attempt yields, to ensure the allocation-gate timer is scheduled. */ - resched_after = jiffies + msecs_to_jiffies(CONFIG_KFENCE_SAMPLE_INTERVAL); + resched_after = jiffies + msecs_to_jiffies(kfence_sample_interval); do { if (test_cache) alloc = kmem_cache_alloc(test_cache, gfp); @@ -608,7 +608,7 @@ static void test_gfpzero(struct kunit *test) int i; /* Skip if we think it'd take too long. */ - KFENCE_TEST_REQUIRES(test, CONFIG_KFENCE_SAMPLE_INTERVAL <= 100); + KFENCE_TEST_REQUIRES(test, kfence_sample_interval <= 100); setup_test_cache(test, size, 0, NULL); buf1 = test_alloc(test, size, GFP_KERNEL, ALLOCATE_ANY); @@ -739,7 +739,7 @@ static void test_memcache_alloc_bulk(struct kunit *test) * 100x the sample interval should be more than enough to ensure we get * a KFENCE allocation eventually. */ - timeout = jiffies + msecs_to_jiffies(100 * CONFIG_KFENCE_SAMPLE_INTERVAL); + timeout = jiffies + msecs_to_jiffies(100 * kfence_sample_interval); do { void *objects[100]; int i, num = kmem_cache_alloc_bulk(test_cache, GFP_ATOMIC, ARRAY_SIZE(objects), -- 2.18.0.huawei.25

4 years, 6 months

[PATCH v2] kfence: Make test case compatible with run time set sample interval

by Peng Liu

The parameter kfence_sample_interval can be set via boot parameter and late shell command, which is convenient for automatical tests and KFENCE parameter optimation. However, KFENCE test case just use compile time CONFIG_KFENCE_SAMPLE_INTERVAL, this will make KFENCE test case not run as user desired. This patch will make KFENCE test case compatible with run-time-set sample interval. v1->v2: - Use EXPORT_SYMBOL_GPL replace EXPORT_SYMBOL Signed-off-by: Peng Liu <liupeng256(a)huawei.com> --- include/linux/kfence.h | 2 ++ mm/kfence/core.c | 3 ++- mm/kfence/kfence_test.c | 8 ++++---- 3 files changed, 8 insertions(+), 5 deletions(-) diff --git a/include/linux/kfence.h b/include/linux/kfence.h index 4b5e3679a72c..f49e64222628 100644 --- a/include/linux/kfence.h +++ b/include/linux/kfence.h @@ -17,6 +17,8 @@ #include <linux/atomic.h> #include <linux/static_key.h> +extern unsigned long kfence_sample_interval; + /* * We allocate an even number of pages, as it simplifies calculations to map * address to metadata indices; effectively, the very first page serves as an diff --git a/mm/kfence/core.c b/mm/kfence/core.c index 5ad40e3add45..13128fa13062 100644 --- a/mm/kfence/core.c +++ b/mm/kfence/core.c @@ -47,7 +47,8 @@ static bool kfence_enabled __read_mostly; -static unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE_INTERVAL; +unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE_INTERVAL; +EXPORT_SYMBOL_GPL(kfence_sample_interval); /* Export for test modules. */ #ifdef MODULE_PARAM_PREFIX #undef MODULE_PARAM_PREFIX diff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c index a22b1af85577..50dbb815a2a8 100644 --- a/mm/kfence/kfence_test.c +++ b/mm/kfence/kfence_test.c @@ -268,13 +268,13 @@ static void *test_alloc(struct kunit *test, size_t size, gfp_t gfp, enum allocat * 100x the sample interval should be more than enough to ensure we get * a KFENCE allocation eventually. */ - timeout = jiffies + msecs_to_jiffies(100 * CONFIG_KFENCE_SAMPLE_INTERVAL); + timeout = jiffies + msecs_to_jiffies(100 * kfence_sample_interval); /* * Especially for non-preemption kernels, ensure the allocation-gate * timer can catch up: after @resched_after, every failed allocation * attempt yields, to ensure the allocation-gate timer is scheduled. */ - resched_after = jiffies + msecs_to_jiffies(CONFIG_KFENCE_SAMPLE_INTERVAL); + resched_after = jiffies + msecs_to_jiffies(kfence_sample_interval); do { if (test_cache) alloc = kmem_cache_alloc(test_cache, gfp); @@ -608,7 +608,7 @@ static void test_gfpzero(struct kunit *test) int i; /* Skip if we think it'd take too long. */ - KFENCE_TEST_REQUIRES(test, CONFIG_KFENCE_SAMPLE_INTERVAL <= 100); + KFENCE_TEST_REQUIRES(test, kfence_sample_interval <= 100); setup_test_cache(test, size, 0, NULL); buf1 = test_alloc(test, size, GFP_KERNEL, ALLOCATE_ANY); @@ -739,7 +739,7 @@ static void test_memcache_alloc_bulk(struct kunit *test) * 100x the sample interval should be more than enough to ensure we get * a KFENCE allocation eventually. */ - timeout = jiffies + msecs_to_jiffies(100 * CONFIG_KFENCE_SAMPLE_INTERVAL); + timeout = jiffies + msecs_to_jiffies(100 * kfence_sample_interval); do { void *objects[100]; int i, num = kmem_cache_alloc_bulk(test_cache, GFP_ATOMIC, ARRAY_SIZE(objects), -- 2.18.0.huawei.25

4 years, 6 months

[PATCH] dma-buf: heaps: Fix potential spectre v1 gadget

by Jordy Zomer

It appears like nr could be a Spectre v1 gadget as it's supplied by a user and used as an array index. Prevent the contents of kernel memory from being leaked to userspace via speculative execution by using array_index_nospec. Signed-off-by: Jordy Zomer <jordy(a)pwning.systems> --- drivers/dma-buf/dma-heap.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c index 56bf5ad01ad5..8f5848aa144f 100644 --- a/drivers/dma-buf/dma-heap.c +++ b/drivers/dma-buf/dma-heap.c @@ -14,6 +14,7 @@ #include <linux/xarray.h> #include <linux/list.h> #include <linux/slab.h> +#include <linux/nospec.h> #include <linux/uaccess.h> #include <linux/syscalls.h> #include <linux/dma-heap.h> @@ -135,6 +136,7 @@ static long dma_heap_ioctl(struct file *file, unsigned int ucmd, if (nr >= ARRAY_SIZE(dma_heap_ioctl_cmds)) return -EINVAL; + nr = array_index_nospec(nr, ARRAY_SIZE(dma_heap_ioctl_cmds)); /* Get the kernel ioctl cmd that matches */ kcmd = dma_heap_ioctl_cmds[nr]; -- 2.27.0

4 years, 6 months

[PATCH] dma-resv: some doc polish for iterators

by Daniel Vetter

Hammer it a bit more in that iterators can be restarted and when that matters, plus suggest to prefer the locked version whenver. Also delete the two leftover kerneldoc for static functions plus sprinkle some more links while at it. Signed-off-by: Daniel Vetter <daniel.vetter(a)intel.com> Cc: Sumit Semwal <sumit.semwal(a)linaro.org> Cc: "Christian König" <christian.koenig(a)amd.com> Cc: linux-media(a)vger.kernel.org Cc: linaro-mm-sig(a)lists.linaro.org --- drivers/dma-buf/dma-resv.c | 26 ++++++++++++-------------- include/linux/dma-resv.h | 13 ++++++++++++- 2 files changed, 24 insertions(+), 15 deletions(-) diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c index 9eb2baa387d4..1453b664c405 100644 --- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -323,12 +323,6 @@ void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence) } EXPORT_SYMBOL(dma_resv_add_excl_fence); -/** - * dma_resv_iter_restart_unlocked - restart the unlocked iterator - * @cursor: The dma_resv_iter object to restart - * - * Restart the unlocked iteration by initializing the cursor object. - */ static void dma_resv_iter_restart_unlocked(struct dma_resv_iter *cursor) { cursor->seq = read_seqcount_begin(&cursor->obj->seq); @@ -344,14 +338,6 @@ static void dma_resv_iter_restart_unlocked(struct dma_resv_iter *cursor) cursor->is_restarted = true; } -/** - * dma_resv_iter_walk_unlocked - walk over fences in a dma_resv obj - * @cursor: cursor to record the current position - * - * Return all the fences in the dma_resv object which are not yet signaled. - * The returned fence has an extra local reference so will stay alive. - * If a concurrent modify is detected the whole iteration is started over again. - */ static void dma_resv_iter_walk_unlocked(struct dma_resv_iter *cursor) { struct dma_resv *obj = cursor->obj; @@ -387,6 +373,12 @@ static void dma_resv_iter_walk_unlocked(struct dma_resv_iter *cursor) * dma_resv_iter_first_unlocked - first fence in an unlocked dma_resv obj. * @cursor: the cursor with the current position * + * Subsequent fences are iterated with dma_resv_iter_next_unlocked(). + * + * Beware that the iterator can be restarted. Code which accumulates statistics + * or similar needs to check for this with dma_resv_iter_is_restarted(). For + * this reason prefer the locked dma_resv_iter_first() whenver possible. + * * Returns the first fence from an unlocked dma_resv obj. */ struct dma_fence *dma_resv_iter_first_unlocked(struct dma_resv_iter *cursor) @@ -406,6 +398,10 @@ EXPORT_SYMBOL(dma_resv_iter_first_unlocked); * dma_resv_iter_next_unlocked - next fence in an unlocked dma_resv obj. * @cursor: the cursor with the current position * + * Beware that the iterator can be restarted. Code which accumulates statistics + * or similar needs to check for this with dma_resv_iter_is_restarted(). For + * this reason prefer the locked dma_resv_iter_next() whenver possible. + * * Returns the next fence from an unlocked dma_resv obj. */ struct dma_fence *dma_resv_iter_next_unlocked(struct dma_resv_iter *cursor) @@ -431,6 +427,8 @@ EXPORT_SYMBOL(dma_resv_iter_next_unlocked); * dma_resv_iter_first - first fence from a locked dma_resv object * @cursor: cursor to record the current position * + * Subsequent fences are iterated with dma_resv_iter_next_unlocked(). + * * Return the first fence in the dma_resv object while holding the * &dma_resv.lock. */ diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h index dbd235ab447f..ebe908592ac3 100644 --- a/include/linux/dma-resv.h +++ b/include/linux/dma-resv.h @@ -153,6 +153,13 @@ struct dma_resv { * struct dma_resv_iter - current position into the dma_resv fences * * Don't touch this directly in the driver, use the accessor function instead. + * + * IMPORTANT + * + * When using the lockless iterators like dma_resv_iter_next_unlocked() or + * dma_resv_for_each_fence_unlocked() beware that the iterator can be restarted. + * Code which accumulates statistics or similar needs to check for this with + * dma_resv_iter_is_restarted(). */ struct dma_resv_iter { /** @obj: The dma_resv object we iterate over */ @@ -243,7 +250,11 @@ static inline bool dma_resv_iter_is_restarted(struct dma_resv_iter *cursor) * &dma_resv.lock and using RCU instead. The cursor needs to be initialized * with dma_resv_iter_begin() and cleaned up with dma_resv_iter_end(). Inside * the iterator a reference to the dma_fence is held and the RCU lock dropped. - * When the dma_resv is modified the iteration starts over again. + * + * Beware that the iterator can be restarted when the struct dma_resv for + * @cursor is modified. Code which accumulates statistics or similar needs to + * check for this with dma_resv_iter_is_restarted(). For this reason prefer the + * lock iterator dma_resv_for_each_fence() whenever possible. */ #define dma_resv_for_each_fence_unlocked(cursor, fence) \ for (fence = dma_resv_iter_first_unlocked(cursor); \ -- 2.33.0

4 years, 6 months

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