On Mon, Apr 29, 2024 at 09:02:16AM -0400, Johannes Weiner wrote:
Christian reports a NULL deref in zswap that he bisected down to the zswap shrinker. The issue also cropped up in the bug trackers of libguestfs [1] and the Red Hat bugzilla [2].
The problem is that when memcg is disabled with the boot time flag, the zswap shrinker might get called with sc->memcg == NULL. This is okay in many places, like the lruvec operations. But it crashes in memcg_page_state() - which is only used due to the non-node accounting of cgroup's the zswap memory to begin with.
Nhat spotted that the memcg can be NULL in the memcg-disabled case, and I was then able to reproduce the crash locally as well.
[1] https://github.com/libguestfs/libguestfs/issues/139 [2] https://bugzilla.redhat.com/show_bug.cgi?id=2275252
Link: https://lkml.kernel.org/r/20240418124043.GC1055428@cmpxchg.org Link: https://lkml.kernel.org/r/20240417143324.GA1055428@cmpxchg.org Fixes: b5ba474f3f51 ("zswap: shrink zswap pool based on memory pressure") Signed-off-by: Johannes Weiner hannes@cmpxchg.org Reported-by: Christian Heusel christian@heusel.eu Debugged-by: Nhat Pham nphamcs@gmail.com Suggested-by: Nhat Pham nphamcs@gmail.com Tested-by: Christian Heusel christian@heusel.eu Acked-by: Yosry Ahmed yosryahmed@google.com Cc: Chengming Zhou chengming.zhou@linux.dev Cc: Dan Streetman ddstreet@ieee.org Cc: Richard W.M. Jones rjones@redhat.com Cc: Seth Jennings sjenning@redhat.com Cc: Vitaly Wool vitaly.wool@konsulko.com Cc: stable@vger.kernel.org [v6.8] Signed-off-by: Andrew Morton akpm@linux-foundation.org (cherry picked from commit 682886ec69d22363819a83ddddd5d66cb5c791e1) Signed-off-by: Johannes Weiner hannes@cmpxchg.org
mm/zswap.c | 25 ++++++++++++++++--------- 1 file changed, 16 insertions(+), 9 deletions(-)
Now queued up, thanks.
greg k-h