From 03e4e0a9e02cf703da331ff6cfd57d0be9bf5692 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Tue, 14 Nov 2017 16:27:19 +0000 Subject: dma-buf/fence: Fix lock inversion within dma-fence-array MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Suggested-by: Rob Clark References: 1476635975-21981-1-git-send-email-robdclark@gmail.com Signed-off-by: Chris Wilson Cc: Rob Clark Cc: Gustavo Padovan Cc: Sumit Semwal Cc: Christian König Reviewed-by: Christian König Signed-off-by: Sumit Semwal Link: https://patchwork.freedesktop.org/patch/msgid/20171114162719.30958-1-chris@chris-wilson.co.uk --- drivers/dma-buf/dma-fence-array.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) (limited to 'drivers/dma-buf/dma-fence-array.c') diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c index 0350829ba62e..dd1edfb27b61 100644 --- a/drivers/dma-buf/dma-fence-array.c +++ b/drivers/dma-buf/dma-fence-array.c @@ -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) { @@ -39,8 +47,9 @@ 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); - dma_fence_put(&array->base); + irq_work_queue(&array->work); + else + dma_fence_put(&array->base); } static bool dma_fence_array_enable_signaling(struct dma_fence *fence) @@ -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); -- cgit v1.2.3