This is a note to let you know that I've just added the patch titled
mm: zswap: fix shrinker NULL crash with cgroup_disable=memory
to the 6.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-zswap-fix-shrinker-null-crash-with-cgroup_disable-memory.patch
and it can be found in the queue-6.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 682886ec69d22363819a83ddddd5d66cb5c791e1 Mon Sep 17 00:00:00 2001
From: Johannes Weiner <hannes@xxxxxxxxxxx>
Date: Thu, 18 Apr 2024 08:26:28 -0400
Subject: mm: zswap: fix shrinker NULL crash with cgroup_disable=memory
From: Johannes Weiner <hannes@xxxxxxxxxxx>
commit 682886ec69d22363819a83ddddd5d66cb5c791e1 upstream.
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>
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/zswap.c | 25 ++++++++++++++++---------
1 file changed, 16 insertions(+), 9 deletions(-)
Two minor conflicts in the else branch:
- zswap_pool_total_size was get_zswap_pool_size() in 6.8
- zswap_nr_stored was pool->nr_stored in 6.8
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -653,15 +653,22 @@ static unsigned long zswap_shrinker_coun
if (!gfp_has_io_fs(sc->gfp_mask))
return 0;
-#ifdef CONFIG_MEMCG_KMEM
- mem_cgroup_flush_stats(memcg);
- nr_backing = memcg_page_state(memcg, MEMCG_ZSWAP_B) >> PAGE_SHIFT;
- nr_stored = memcg_page_state(memcg, MEMCG_ZSWAPPED);
-#else
- /* use pool stats instead of memcg stats */
- nr_backing = get_zswap_pool_size(pool) >> PAGE_SHIFT;
- nr_stored = atomic_read(&pool->nr_stored);
-#endif
+ /*
+ * For memcg, use the cgroup-wide ZSWAP stats since we don't
+ * have them per-node and thus per-lruvec. Careful if memcg is
+ * runtime-disabled: we can get sc->memcg == NULL, which is ok
+ * for the lruvec, but not for memcg_page_state().
+ *
+ * Without memcg, use the zswap pool-wide metrics.
+ */
+ if (!mem_cgroup_disabled()) {
+ mem_cgroup_flush_stats(memcg);
+ nr_backing = memcg_page_state(memcg, MEMCG_ZSWAP_B) >> PAGE_SHIFT;
+ nr_stored = memcg_page_state(memcg, MEMCG_ZSWAPPED);
+ } else {
+ nr_backing = get_zswap_pool_size(pool) >> PAGE_SHIFT;
+ nr_stored = atomic_read(&pool->nr_stored);
+ }
if (!nr_stored)
return 0;
Patches currently in stable-queue which might be from hannes@xxxxxxxxxxx are
queue-6.8/mm-zswap-fix-shrinker-null-crash-with-cgroup_disable-memory.patch
