dma-buf/fence: Fix lock inversion within dma-fence-array (03e4e0a9) · Commits · 戴 / test

Ages ago Rob Clark noted, "Currently with fence-array, we have a potential deadlock situation. If we fence_add_callback() on an array-fence, the array-fence's lock is acquired first, and in it's ->enable_signaling() callback, it will install cbs on it's array-member fences, so the array-member's lock is acquired second. But in the signal path, the array-member's lock is acquired first, and the array-fence's lock acquired second." Rob proposed either extensive changes to dma-fence to unnest the fence-array signaling, or to defer the signaling onto a workqueue. This is a more refined version of the later, that should keep the latency of the fence signaling to a minimum by using an irq-work, which is executed asap. Reported-by:

Rob Clark <robdclark@gmail.com> Suggested-by:

Rob Clark <robdclark@gmail.com> References: 1476635975-21981-1-git-send-email-robdclark@gmail.com Signed-off-by:

Chris Wilson <chris@chris-wilson.co.uk> Cc: Rob Clark <robdclark@gmail.com> Cc: Gustavo Padovan <gustavo.padovan@collabora.co.uk> Cc: Sumit Semwal <sumit.semwal@linaro.org> Cc: Christian König <christian.koenig@amd.com> Reviewed-by:

Christian König <christian.koenig@amd.com> Signed-off-by:

Sumit Semwal <sumit.semwal@linaro.org> Link: https://patchwork.freedesktop.org/patch/msgid/20171114162719.30958-1-chris@chris-wilson.co.uk

drivers/base/Kconfig

+1 −0

Original line number	Diff line number	Diff line
		@@ -244,6 +244,7 @@ config DMA_SHARED_BUFFER
		bool
		default n
		select ANON_INODES
		select IRQ_WORK
		help
		This option enables the framework for buffer-sharing between
		multiple drivers. A buffer is associated with a file using driver

drivers/dma-buf/dma-fence-array.c

+12 −2

Original line number	Diff line number	Diff line
		@@ -31,6 +31,14 @@ static const char dma_fence_array_get_timeline_name(struct dma_fence fence)
		return "unbound";
		}

		static void irq_dma_fence_array_work(struct irq_work *wrk)
		{
		struct dma_fence_array array = container_of(wrk, typeof(array), work);

		dma_fence_signal(&array->base);
		dma_fence_put(&array->base);
		}

		static void dma_fence_array_cb_func(struct dma_fence *f,
		struct dma_fence_cb *cb)
		{
		@@ -39,7 +47,8 @@ static void dma_fence_array_cb_func(struct dma_fence *f,
		struct dma_fence_array *array = array_cb->array;

		if (atomic_dec_and_test(&array->num_pending))
		dma_fence_signal(&array->base);
		irq_work_queue(&array->work);
		else
		dma_fence_put(&array->base);
		}

		@@ -136,6 +145,7 @@ struct dma_fence_array *dma_fence_array_create(int num_fences,
		spin_lock_init(&array->lock);
		dma_fence_init(&array->base, &dma_fence_array_ops, &array->lock,
		context, seqno);
		init_irq_work(&array->work, irq_dma_fence_array_work);

		array->num_fences = num_fences;
		atomic_set(&array->num_pending, signal_on_any ? 1 : num_fences);

include/linux/dma-fence-array.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -21,6 +21,7 @@
		#define __LINUX_DMA_FENCE_ARRAY_H

		#include <linux/dma-fence.h>
		#include <linux/irq_work.h>

		/**
		* struct dma_fence_array_cb - callback helper for fence array
		@@ -47,6 +48,8 @@ struct dma_fence_array {
		unsigned num_fences;
		atomic_t num_pending;
		struct dma_fence **fences;

		struct irq_work work;
		};

		extern const struct dma_fence_ops dma_fence_array_ops;

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