From 312b559d9e61b473b39d3dc05fe0db43c2df60fb Mon Sep 17 00:00:00 2001 From: Tetsuo Handa Date: Sun, 3 Aug 2014 20:02:03 +0900 Subject: [PATCH] drm/ttm: Fix possible stack overflow by recursive shrinker calls. commit 71336e011d1d2312bcbcaa8fcec7365024f3a95d upstream. 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 Signed-off-by: Dave Airlie [bwh: Backported to 3.2: - Adjust context - Change return value in the contended case to follow the old shrinker API] Signed-off-by: Ben Hutchings --- drivers/gpu/drm/ttm/ttm_page_alloc.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/ttm/ttm_page_alloc.c b/drivers/gpu/drm/ttm/ttm_page_alloc.c index 9e4313edad27b..508c64ce5d9e8 100644 --- a/drivers/gpu/drm/ttm/ttm_page_alloc.c +++ b/drivers/gpu/drm/ttm/ttm_page_alloc.c @@ -398,13 +398,18 @@ static int ttm_pool_get_num_unused_pages(void) static int ttm_pool_mm_shrink(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; - pool_offset = pool_offset % NUM_POOLS; + if (shrink_pages == 0) + goto out; + if (!mutex_trylock(&lock)) + return -1; + 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; @@ -413,6 +418,8 @@ static int ttm_pool_mm_shrink(struct shrinker *shrink, pool = &_manager->pools[(i + pool_offset)%NUM_POOLS]; shrink_pages = ttm_page_pool_free(pool, nr_free); } + mutex_unlock(&lock); +out: /* return estimated number of unused pages in pool */ return ttm_pool_get_num_unused_pages(); } -- 2.47.3