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 --- include/linux/dma-fence-array.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'include/linux/dma-fence-array.h') diff --git a/include/linux/dma-fence-array.h b/include/linux/dma-fence-array.h index 332a5420243c..bc8940ca280d 100644 --- a/include/linux/dma-fence-array.h +++ b/include/linux/dma-fence-array.h @@ -21,6 +21,7 @@ #define __LINUX_DMA_FENCE_ARRAY_H #include +#include /** * 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; -- cgit