linux/drivers/staging/zcache
Seth Jennings 6d7d9798ad staging: zcache: fix cleancache race condition with shrinker
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>
Cc: stable <stable@vger.kernel.org>
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>
2012-09-05 12:06:48 -07:00
..
Kconfig staging: zram/zcache: swtich Kconfig dependency from X86 to ZSMALLOC 2012-06-25 10:00:53 -07:00
Makefile staging: fix zcache building 2011-08-02 16:06:18 -07:00
tmem.c staging: zcache: cleanup the code between tmem_obj_init and tmem_obj_find 2012-07-09 11:31:16 -07:00
tmem.h staging/zmem: Use lockdep_assert_held instead of spin_is_locked 2012-03-16 14:47:41 -07:00
zcache-main.c staging: zcache: fix cleancache race condition with shrinker 2012-09-05 12:06:48 -07:00