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authorSeth Jennings <sjenning@linux.vnet.ibm.com>2012-08-29 16:58:45 -0500
committerSimon Shields <keepcalm444@gmail.com>2016-06-12 21:20:20 +1000
commit128faec612bd65b7c7b5318c47d35f4cabbc3060 (patch)
treefa141b7919acaf354c44137a4cd9f3f3dcac24e0
parent912b213927c79feb8254549b13eba41870d56081 (diff)
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staging: zcache: fix cleancache race condition with shrinker
commit 6d7d9798ad5c97ee4e911dd070dc12dc5ae55bd0 upstream. 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. 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. Change-Id: I618a2488d788c15b3e8d74d2831cc5d83ca71abc Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Reviewed-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/staging/zcache/zcache-main.c7
1 files changed, 3 insertions, 4 deletions
diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c
index d781bd0..61cce6b 100644
--- a/drivers/staging/zcache/zcache-main.c
+++ b/drivers/staging/zcache/zcache-main.c
@@ -1259,13 +1259,12 @@ 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;
}
/*