Re: [PATCH 3/5] gpu/drm/ttm: Use mutex_trylock() to avoid deadlock inside shrinker functions.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Sat, May 31, 2014 at 12:00:45PM +0900, Tetsuo Handa wrote:
> >From 4e8d1a83629c5966bfd401c5f2187355624194f2 Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Date: Sat, 31 May 2014 09:59:44 +0900
> Subject: [PATCH 3/5] gpu/drm/ttm: Use mutex_trylock() to avoid deadlock inside 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.
> 
> 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@I-love.SAKURA.ne.jp>
> Cc: stable <stable@kernel.org> [3.3+]
> ---
>  drivers/gpu/drm/ttm/ttm_page_alloc_dma.c |    6 ++++--
>  1 files 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 d8e59f7..620da39 100644
> --- a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
> +++ b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
> @@ -1014,7 +1014,8 @@ 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(&_manager->lock))
> +		return SHRINK_STOP;

Hmm..

/home/konrad/linux/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c: In function ‘ttm_dma_pool_shrink_scan’:
/home/konrad/linux/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c:1015:2: error: invalid use of void expression
  if (!mutex_lock(&_manager->lock))

This is based on v3.15 with these patches.

>  	if (!_manager->npools)
>  		goto out;
>  	pool_offset = ++start_pool % _manager->npools;
> @@ -1047,7 +1048,8 @@ 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;
>  	mutex_unlock(&_manager->lock);
> -- 
> 1.7.1
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