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@xxxxxxxxxxx > Link: https://lkml.kernel.org/r/20240417143324.GA1055428@xxxxxxxxxxx > Fixes: b5ba474f3f51 ("zswap: shrink zswap pool based on memory pressure") > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> > Reported-by: Christian Heusel <christian@xxxxxxxxx> > Debugged-by: Nhat Pham <nphamcs@xxxxxxxxx> > Suggested-by: Nhat Pham <nphamcs@xxxxxxxxx> > Tested-by: Christian Heusel <christian@xxxxxxxxx> > Acked-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx> > Cc: Chengming Zhou <chengming.zhou@xxxxxxxxx> > Cc: Dan Streetman <ddstreet@xxxxxxxx> > Cc: Richard W.M. Jones <rjones@xxxxxxxxxx> > Cc: Seth Jennings <sjenning@xxxxxxxxxx> > Cc: Vitaly Wool <vitaly.wool@xxxxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> [v6.8] > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > (cherry picked from commit 682886ec69d22363819a83ddddd5d66cb5c791e1) > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> > --- > mm/zswap.c | 25 ++++++++++++++++--------- > 1 file changed, 16 insertions(+), 9 deletions(-) Now queued up, thanks. greg k-h
