| From | Greg Kroah-Hartman <> | Subject | [ 060/262] staging: zcache: fix cleancache race condition with shrinker | Date | Fri, 28 Sep 2012 11:49:49 -0700 |
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From: Greg KH <gregkh@linuxfoundation.org>
3.5-stable review patch. If anyone has any objections, please let me know.
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From: Seth Jennings <sjenning@linux.vnet.ibm.com>
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.
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>
--- drivers/staging/zcache/zcache-main.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-)
--- 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_fre 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; } /*
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