cc'ing dri-devel.
> >From e314a1a1583e585d062dfc30c8aad8bf5380510b Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Date: Mon, 19 May 2014 18:43:21 +0900
> Subject: [PATCH] gpu/drm/ttm: Use mutex_lock_killable() for shrinker functions.
>
> 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.
>
> I added debug printk() and observed that many threads are blocked for more
> than 10 seconds at ttm_dma_pool_shrink_count()/ttm_dma_pool_shrink_scan()
> functions. Since the kswapd can call these functions later, the current
> thread can return from these functions as soon as chosen by the OOM killer.
>
> This patch changes "mutex_lock();" to "if (mutex_lock_killable()) return ...;"
> so that any threads can promptly give up. (By the way, as far as I tested,
> changing to "if (!mutex_trylock()) return ...;" likely shortens the duration
> of stall. Maybe we don't need to wait for mutex if someone is already calling
> these functions.)
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> ---
> 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 1b79bf0..f75dab8 100644
> --- a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
> +++ b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
> @@ -1012,7 +1012,8 @@ ttm_dma_pool_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
> if (list_empty(&_manager->pools))
> return SHRINK_STOP;
>
> - mutex_lock(&_manager->lock);
> + if (mutex_lock_killable(&_manager->lock))
> + return SHRINK_STOP;
> pool_offset = pool_offset % _manager->npools;
> list_for_each_entry(p, &_manager->pools, pools) {
> unsigned nr_free;
> @@ -1043,7 +1044,8 @@ 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_lock_killable(&_manager->lock))
> + return 0;
> list_for_each_entry(p, &_manager->pools, pools)
> count += p->pool->npages_free;
> mutex_unlock(&_manager->lock);
>
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