>From 16009d9def2c3087772e6c9dbec6c60950ae768b Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp>
Date: Sun, 3 Aug 2014 20:02:03 +0900
Subject: [PATCH 4/5] gpu/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-ker...@i-love.sakura.ne.jp>
Cc: stable <sta...@kernel.org> [2.6.35+]
---
drivers/gpu/drm/ttm/ttm_page_alloc.c | 10 +++++++---
1 files changed, 7 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/ttm/ttm_page_alloc.c
b/drivers/gpu/drm/ttm/ttm_page_alloc.c
index beb8e75..edb8315 100644
--- a/drivers/gpu/drm/ttm/ttm_page_alloc.c
+++ b/drivers/gpu/drm/ttm/ttm_page_alloc.c
@@ -391,14 +391,17 @@ out:
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;
}
--
1.7.1
--
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