From: Chris Wilson <chris@chris-wilson.co.uk> To: dri-devel@lists.freedesktop.org Cc: intel-gfx@lists.freedesktop.org, Chris Wilson <chris@chris-wilson.co.uk>, Daniel Vetter <daniel.vetter@ffwll.ch>, Sumit Semwal <sumit.semwal@linaro.org>, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org Subject: [PATCH 06/11] dma-buf: Introduce fence_get_rcu_safe() Date: Mon, 29 Aug 2016 08:08:29 +0100 [thread overview] Message-ID: <20160829070834.22296-6-chris@chris-wilson.co.uk> (raw) In-Reply-To: <20160829070834.22296-1-chris@chris-wilson.co.uk> This variant of fence_get_rcu() takes an RCU protected pointer to a fence and carefully returns a reference to the fence ensuring that it is not reallocated as it does. This is required when mixing fences and SLAB_DESTROY_BY_RCU - although it serves a more pedagogical function atm Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Sumit Semwal <sumit.semwal@linaro.org> Cc: linux-media@vger.kernel.org Cc: dri-devel@lists.freedesktop.org Cc: linaro-mm-sig@lists.linaro.org --- include/linux/fence.h | 56 ++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 51 insertions(+), 5 deletions(-) diff --git a/include/linux/fence.h b/include/linux/fence.h index 0d763053f97a..c9c5ba98c302 100644 --- a/include/linux/fence.h +++ b/include/linux/fence.h @@ -183,6 +183,16 @@ void fence_release(struct kref *kref); void fence_free(struct fence *fence); /** + * fence_put - decreases refcount of the fence + * @fence: [in] fence to reduce refcount of + */ +static inline void fence_put(struct fence *fence) +{ + if (fence) + kref_put(&fence->refcount, fence_release); +} + +/** * fence_get - increases refcount of the fence * @fence: [in] fence to increase refcount of * @@ -210,13 +220,49 @@ static inline struct fence *fence_get_rcu(struct fence *fence) } /** - * fence_put - decreases refcount of the fence - * @fence: [in] fence to reduce refcount of + * fence_get_rcu_safe - acquire a reference to an RCU tracked fence + * @fence: [in] pointer to fence to increase refcount of + * + * Function returns NULL if no refcount could be obtained, or the fence. + * This function handles acquiring a reference to a fence that may be + * reallocated within the RCU grace period (such as with SLAB_DESTROY_BY_RCU), + * so long as the caller is using RCU on the pointer to the fence. + * + * An alternative mechanism is to employ a seqlock to protect a bunch of + * fences, such as used by struct reservation_object. When using a seqlock, + * the seqlock must be taken before and checked after a reference to the + * fence is acquired (as shown here). + * + * The caller is required to hold the RCU read lock. */ -static inline void fence_put(struct fence *fence) +static inline struct fence *fence_get_rcu_safe(struct fence * __rcu *fencep) { - if (fence) - kref_put(&fence->refcount, fence_release); + do { + struct fence *fence; + + fence = rcu_dereference(*fencep); + if (!fence || !fence_get_rcu(fence)) + return NULL; + + /* The atomic_inc_not_zero() inside fence_get_rcu() + * provides a full memory barrier upon success (such as now). + * This is paired with the write barrier from assigning + * to the __rcu protected fence pointer so that if that + * pointer still matches the current fence, we know we + * have successfully acquire a reference to it. If it no + * longer matches, we are holding a reference to some other + * reallocated pointer. This is possible if the allocator + * is using a freelist like SLAB_DESTROY_BY_RCU where the + * fence remains valid for the RCU grace period, but it + * may be reallocated. When using such allocators, we are + * responsible for ensuring the reference we get is to + * the right fence, as below. + */ + if (fence == rcu_access_pointer(*fencep)) + return rcu_pointer_handoff(fence); + + fence_put(fence); + } while (1); } int fence_signal(struct fence *fence); -- 2.9.3
WARNING: multiple messages have this Message-ID (diff)
From: Chris Wilson <chris@chris-wilson.co.uk> To: dri-devel@lists.freedesktop.org Cc: Daniel Vetter <daniel.vetter@ffwll.ch>, intel-gfx@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, Sumit Semwal <sumit.semwal@linaro.org>, linux-media@vger.kernel.org Subject: [PATCH 06/11] dma-buf: Introduce fence_get_rcu_safe() Date: Mon, 29 Aug 2016 08:08:29 +0100 [thread overview] Message-ID: <20160829070834.22296-6-chris@chris-wilson.co.uk> (raw) In-Reply-To: <20160829070834.22296-1-chris@chris-wilson.co.uk> This variant of fence_get_rcu() takes an RCU protected pointer to a fence and carefully returns a reference to the fence ensuring that it is not reallocated as it does. This is required when mixing fences and SLAB_DESTROY_BY_RCU - although it serves a more pedagogical function atm Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Sumit Semwal <sumit.semwal@linaro.org> Cc: linux-media@vger.kernel.org Cc: dri-devel@lists.freedesktop.org Cc: linaro-mm-sig@lists.linaro.org --- include/linux/fence.h | 56 ++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 51 insertions(+), 5 deletions(-) diff --git a/include/linux/fence.h b/include/linux/fence.h index 0d763053f97a..c9c5ba98c302 100644 --- a/include/linux/fence.h +++ b/include/linux/fence.h @@ -183,6 +183,16 @@ void fence_release(struct kref *kref); void fence_free(struct fence *fence); /** + * fence_put - decreases refcount of the fence + * @fence: [in] fence to reduce refcount of + */ +static inline void fence_put(struct fence *fence) +{ + if (fence) + kref_put(&fence->refcount, fence_release); +} + +/** * fence_get - increases refcount of the fence * @fence: [in] fence to increase refcount of * @@ -210,13 +220,49 @@ static inline struct fence *fence_get_rcu(struct fence *fence) } /** - * fence_put - decreases refcount of the fence - * @fence: [in] fence to reduce refcount of + * fence_get_rcu_safe - acquire a reference to an RCU tracked fence + * @fence: [in] pointer to fence to increase refcount of + * + * Function returns NULL if no refcount could be obtained, or the fence. + * This function handles acquiring a reference to a fence that may be + * reallocated within the RCU grace period (such as with SLAB_DESTROY_BY_RCU), + * so long as the caller is using RCU on the pointer to the fence. + * + * An alternative mechanism is to employ a seqlock to protect a bunch of + * fences, such as used by struct reservation_object. When using a seqlock, + * the seqlock must be taken before and checked after a reference to the + * fence is acquired (as shown here). + * + * The caller is required to hold the RCU read lock. */ -static inline void fence_put(struct fence *fence) +static inline struct fence *fence_get_rcu_safe(struct fence * __rcu *fencep) { - if (fence) - kref_put(&fence->refcount, fence_release); + do { + struct fence *fence; + + fence = rcu_dereference(*fencep); + if (!fence || !fence_get_rcu(fence)) + return NULL; + + /* The atomic_inc_not_zero() inside fence_get_rcu() + * provides a full memory barrier upon success (such as now). + * This is paired with the write barrier from assigning + * to the __rcu protected fence pointer so that if that + * pointer still matches the current fence, we know we + * have successfully acquire a reference to it. If it no + * longer matches, we are holding a reference to some other + * reallocated pointer. This is possible if the allocator + * is using a freelist like SLAB_DESTROY_BY_RCU where the + * fence remains valid for the RCU grace period, but it + * may be reallocated. When using such allocators, we are + * responsible for ensuring the reference we get is to + * the right fence, as below. + */ + if (fence == rcu_access_pointer(*fencep)) + return rcu_pointer_handoff(fence); + + fence_put(fence); + } while (1); } int fence_signal(struct fence *fence); -- 2.9.3 _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
next prev parent reply other threads:[~2016-08-29 7:25 UTC|newest] Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-08-29 7:08 [PATCH 01/11] drm/amdgpu: Remove call to reservation_object_test_signaled_rcu before wait Chris Wilson 2016-08-29 7:08 ` [PATCH 02/11] drm/etnaviv: Remove manual " Chris Wilson 2016-09-23 12:55 ` Daniel Vetter 2016-10-05 16:15 ` Sumit Semwal 2016-10-10 13:17 ` Lucas Stach 2016-08-29 7:08 ` [PATCH 03/11] drm/msm: Remove " Chris Wilson 2016-09-23 12:55 ` Daniel Vetter 2016-09-23 13:07 ` [Intel-gfx] " Rob Clark 2016-08-29 7:08 ` [PATCH 04/11] drm/nouveau: " Chris Wilson 2016-09-23 12:55 ` Daniel Vetter 2016-10-05 16:05 ` Sumit Semwal 2016-08-29 7:08 ` [PATCH 05/11] drm/vmwgfx: " Chris Wilson 2016-09-23 12:56 ` Daniel Vetter 2016-10-05 16:11 ` [Intel-gfx] " Sumit Semwal 2016-10-05 17:03 ` Sinclair Yeh 2016-08-29 7:08 ` Chris Wilson [this message] 2016-08-29 7:08 ` [PATCH 06/11] dma-buf: Introduce fence_get_rcu_safe() Chris Wilson 2016-09-23 12:59 ` Daniel Vetter 2016-09-23 12:59 ` Daniel Vetter 2016-09-23 13:34 ` Markus Heiser 2016-09-23 13:34 ` Markus Heiser 2016-08-29 7:08 ` [PATCH 07/11] dma-buf: Restart reservation_object_get_fences_rcu() after writes Chris Wilson 2016-08-29 7:08 ` Chris Wilson 2016-09-23 13:03 ` Daniel Vetter 2016-09-23 13:03 ` Daniel Vetter 2016-08-29 7:08 ` [PATCH 08/11] dma-buf: Restart reservation_object_wait_timeout_rcu() " Chris Wilson 2016-08-29 7:08 ` Chris Wilson 2016-09-23 13:18 ` Daniel Vetter 2016-08-29 7:08 ` [PATCH 09/11] dma-buf: Restart reservation_object_test_signaled_rcu() " Chris Wilson 2016-08-29 7:08 ` Chris Wilson 2016-09-23 13:43 ` Daniel Vetter 2016-09-23 13:43 ` Daniel Vetter 2016-08-29 7:08 ` [PATCH 10/11] dma-buf: Use seqlock to close RCU race in test_signaled_single Chris Wilson 2016-08-29 7:08 ` Chris Wilson 2016-09-23 13:49 ` [Linaro-mm-sig] " Daniel Vetter 2016-09-23 13:49 ` Daniel Vetter 2016-09-23 14:02 ` Chris Wilson 2016-09-25 20:43 ` Daniel Vetter 2016-09-25 20:43 ` Daniel Vetter 2016-08-29 7:08 ` [PATCH 11/11] dma-buf: Do a fast lockless check for poll with timeout=0 Chris Wilson 2016-08-29 7:08 ` Chris Wilson 2016-08-29 18:16 ` [PATCH] dma-buf/sync-file: Avoid enable fence signaling if poll(.timeout=0) Chris Wilson 2016-08-29 18:16 ` Chris Wilson 2016-08-29 18:26 ` Gustavo Padovan 2016-09-13 14:46 ` Sumit Semwal 2016-09-13 14:46 ` Sumit Semwal 2016-09-15 0:00 ` Rafael Antognolli 2016-09-21 7:26 ` Gustavo Padovan 2016-09-21 11:08 ` Chris Wilson 2016-09-23 13:50 ` [Intel-gfx] [PATCH 11/11] dma-buf: Do a fast lockless check for poll with timeout=0 Daniel Vetter 2016-09-23 13:50 ` Daniel Vetter 2016-09-23 14:15 ` Chris Wilson 2016-09-23 15:06 ` Chris Wilson 2016-09-23 15:06 ` Chris Wilson 2016-09-23 15:20 ` [Intel-gfx] " Chris Wilson 2016-09-23 17:59 ` Christian König 2016-09-23 17:59 ` Christian König 2016-09-25 20:44 ` Daniel Vetter 2016-09-25 20:44 ` Daniel Vetter 2016-08-29 7:50 ` ✗ Fi.CI.BAT: warning for series starting with [01/11] drm/amdgpu: Remove call to reservation_object_test_signaled_rcu before wait Patchwork 2016-08-29 8:20 ` [PATCH 01/11] " Christian König 2016-09-23 12:54 ` Daniel Vetter 2016-10-05 16:03 ` Sumit Semwal
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