Re: [PATCH] staging: zcache: fix cleancache race condition with shrinker
From: Konrad Rzeszutek Wilk <hidden>
Date: 2012-08-30 16:12:04
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On Wed, Aug 29, 2012 at 04:58:45PM -0500, Seth Jennings wrote:
This patch fixes a race condition that results in memory corruption when using cleancache. The race exists between the zcache shrinker handler, shrink_zcache_memory() and cleancache_get_page(). In most cases, the shrinker will both evict a zbpg from its buddy list and flush it from tmem before a cleancache_get_page() occurs on that page. A subsequent cleancache_get_page() will fail in the tmem layer. In the rare case that two occur together and the cleancache_get_page() path gets through the tmem layer before the shrinker path can flush tmem, zbud_decompress() does a check to see if the zbpg is a "zombie", i.e. not on a buddy list, which means the shrinker is in the process of reclaiming it. If the zbpg is a zombie, zbud_decompress() returns -EINVAL. However, this return code is being ignored by the caller, zcache_pampd_get_data_and_free(), which results in the caller of cleancache_get_page() thinking that the page has been properly retrieved when it has not. This patch modifies zcache_pampd_get_data_and_free() to convey the failure up the stack so that the caller of cleancache_get_page() knows the page retrieval failed. --- Based on v3.6-rc3. This needs to be applied to stable trees as well. zcache-main.c was named zcache.c before v3.1, so I'm not sure how you want to handle trees earlier than that. Signed-off-by: Seth Jennings <redacted>
Reviewed-by: Konrad Rzeszutek Wilk <redacted> Thanks for tracking this down!
quoted hunk ↗ jump to hunk
--- drivers/staging/zcache/zcache-main.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-)diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c index c214977..52b43b7 100644 --- a/drivers/staging/zcache/zcache-main.c +++ b/drivers/staging/zcache/zcache-main.c@@ -1251,13 +1251,12 @@ static int zcache_pampd_get_data_and_free(char *data, size_t *bufsize, bool raw, void *pampd, struct tmem_pool *pool, struct tmem_oid *oid, uint32_t index) { - int ret = 0; - BUG_ON(!is_ephemeral(pool)); - zbud_decompress((struct page *)(data), pampd); + if (zbud_decompress((struct page *)(data), pampd) < 0) + return -EINVAL; zbud_free_and_delist((struct zbud_hdr *)pampd); atomic_dec(&zcache_curr_eph_pampd_count); - return ret; + return 0; } /*-- 1.7.9.5
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