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Commit 71336e01 authored by Tetsuo Handa's avatar Tetsuo Handa Committed by Dave Airlie
Browse files

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: default avatarTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: stable <stable@kernel.org> [2.6.35+]
Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
parent 22e71691

drivers/gpu/drm/ttm/ttm_page_alloc.c

+7 −3
Original line number Diff line number Diff line
@@ -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;

}