From 997e954bb05f0a11b6a7023c0bee937ebb52a3f0 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Tue, 14 Nov 2017 16:27:19 +0000 Subject: [PATCH] BACKPORT:dma-buf/fence: Fix lock inversion within dma-fence-array MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 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 Signed-off-by: Jiyu Yang Change-Id: Ia08cb17615ff15b18c208cff2000d92344c9f399 --- drivers/base/Kconfig | 1 + drivers/dma-buf/fence-array.c | 14 ++++++++++++-- include/linux/fence-array.h | 3 +++ 3 files changed, 16 insertions(+), 2 deletions(-) diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig index 0651010..4fe2d75 100644 --- a/drivers/base/Kconfig +++ b/drivers/base/Kconfig @@ -247,6 +247,7 @@ 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 diff --git a/drivers/dma-buf/fence-array.c b/drivers/dma-buf/fence-array.c index f1989fc..f855bd9 100644 --- a/drivers/dma-buf/fence-array.c +++ b/drivers/dma-buf/fence-array.c @@ -33,6 +33,14 @@ static const char *fence_array_get_timeline_name(struct fence *fence) return "unbound"; } +static void irq_fence_array_work(struct irq_work *wrk) +{ + struct fence_array *array = container_of(wrk, typeof(*array), work); + + fence_signal(&array->base); + fence_put(&array->base); +} + static void fence_array_cb_func(struct fence *f, struct fence_cb *cb) { struct fence_array_cb *array_cb = @@ -40,8 +48,9 @@ static void fence_array_cb_func(struct fence *f, struct fence_cb *cb) struct fence_array *array = array_cb->array; if (atomic_dec_and_test(&array->num_pending)) - fence_signal(&array->base); - fence_put(&array->base); + irq_work_queue(&array->work); + else + fence_put(&array->base); } static bool fence_array_enable_signaling(struct fence *fence) @@ -135,6 +144,7 @@ struct fence_array *fence_array_create(int num_fences, struct fence **fences, spin_lock_init(&array->lock); fence_init(&array->base, &fence_array_ops, &array->lock, context, seqno); + init_irq_work(&array->work, irq_fence_array_work); array->num_fences = num_fences; atomic_set(&array->num_pending, signal_on_any ? 1 : num_fences); diff --git a/include/linux/fence-array.h b/include/linux/fence-array.h index a44794e..318342f 100644 --- a/include/linux/fence-array.h +++ b/include/linux/fence-array.h @@ -21,6 +21,7 @@ #define __LINUX_FENCE_ARRAY_H #include +#include /** * struct fence_array_cb - callback helper for fence array @@ -47,6 +48,8 @@ struct fence_array { unsigned num_fences; atomic_t num_pending; struct fence **fences; + + struct irq_work work; }; extern const struct fence_ops fence_array_ops; -- 2.7.4