[PATCH 3.12 128/142] drm/ttm: Use mutex_trylock() to avoid deadlock inside shrinker functions.

From: Jiri Slaby
Date: Fri Sep 26 2014 - 05:51:38 EST

From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>

3.12-stable review patch. If anyone has any objections, please let me know.


commit 22e71691fd54c637800d10816bbeba9cf132d218 upstream.

I can observe that RHEL7 environment stalls with 100% CPU usage when a
certain type of memory pressure is given. While the shrinker functions
are called by shrink_slab() before the OOM killer is triggered, the stall
lasts for many minutes.

One of reasons of this stall is that
ttm_dma_pool_shrink_count()/ttm_dma_pool_shrink_scan() are called and
are blocked at mutex_lock(&_manager->lock). GFP_KERNEL allocation with
_manager->lock held causes someone (including kswapd) to deadlock when
these functions are called due to memory pressure. This patch changes
"mutex_lock();" to "if (!mutex_trylock()) return ...;" in order to
avoid deadlock.

Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
drivers/gpu/drm/ttm/ttm_page_alloc_dma.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
index 5d49274afd0e..629e344dad1e 100644
--- a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
+++ b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
@@ -1013,7 +1013,8 @@ ttm_dma_pool_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
if (list_empty(&_manager->pools))

- mutex_lock(&_manager->lock);
+ if (!mutex_trylock(&_manager->lock))
+ return SHRINK_STOP;
if (!_manager->npools)
goto out;
pool_offset = ++start_pool % _manager->npools;
@@ -1046,7 +1047,8 @@ ttm_dma_pool_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
struct device_pools *p;
unsigned long count = 0;

- mutex_lock(&_manager->lock);
+ if (!mutex_trylock(&_manager->lock))
+ return 0;
list_for_each_entry(p, &_manager->pools, pools)
count += p->pool->npages_free;

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