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 <sjenning@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Thanks for tracking this down!
> ---
> 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
>
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>