From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Sun, 3 Aug 2014 11:01:10 +0000 (+0900)
Subject: drm/ttm: Use mutex_trylock() to avoid deadlock inside shrinker functions.
X-Git-Tag: omap-for-v3.17/fixes-against-rc2~125^2~11
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=22e71691fd54c637800d10816bbeba9cf132d218;p=pandora-kernel.git

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+]
Signed-off-by: Dave Airlie <airlied@redhat.com>
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