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drm/ttm: Fix possible stack overflow by recursive shrinker calls. 

While ttm_dma_pool_shrink_scan() tries to take mutex before doing GFP_KERNEL
allocation, ttm_pool_shrink_scan() does not do it. This can result in stack
overflow if kmalloc() in ttm_page_pool_free() triggered recursion due to
memory pressure.

  shrink_slab()
  => ttm_pool_shrink_scan()
     => ttm_page_pool_free()
        => kmalloc(GFP_KERNEL)
           => shrink_slab()
              => ttm_pool_shrink_scan()
                 => ttm_page_pool_free()
                    => kmalloc(GFP_KERNEL)

Change ttm_pool_shrink_scan() to do like ttm_dma_pool_shrink_scan() does.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: stable <stable@kernel.org> [2.6.35+]
Signed-off-by: Dave Airlie <airlied@redhat.com>
This commit is contained in:
Tetsuo Handa 2014-08-03 20:02:03 +09:00 committed by Dave Airlie
parent 22e71691fd
commit 71336e011d
1 changed files with 7 additions and 3 deletions
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10
drivers/gpu/drm/ttm/ttm_page_alloc.c
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@ -391,14 +391,17 @@ static int ttm_page_pool_free(struct ttm_page_pool *pool, unsigned nr_free)
static unsigned long
ttm_pool_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
{
static atomic_t start_pool = ATOMIC_INIT(0);
static DEFINE_MUTEX(lock);
static unsigned start_pool;
unsigned i;
unsigned pool_offset = atomic_add_return(1, &start_pool);
unsigned pool_offset;
struct ttm_page_pool *pool;
int shrink_pages = sc->nr_to_scan;
unsigned long freed = 0;
pool_offset = pool_offset % NUM_POOLS;
if (!mutex_trylock(&lock))
return SHRINK_STOP;
pool_offset = ++start_pool % NUM_POOLS;
/* select start pool in round robin fashion */
for (i = 0; i < NUM_POOLS; ++i) {
unsigned nr_free = shrink_pages;
@ -408,6 +411,7 @@ ttm_pool_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
shrink_pages = ttm_page_pool_free(pool, nr_free);
freed += nr_free - shrink_pages;
}
mutex_unlock(&lock);
return freed;
}