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authorJohannes Weiner <hannes@cmpxchg.org>2024-04-18 08:26:28 -0400
committerAndrew Morton <akpm@linux-foundation.org>2024-04-24 19:34:26 -0700
commit682886ec69d22363819a83ddddd5d66cb5c791e1 (patch)
tree94594803c09620a99b5a964ab42d276d03a3f39b /mm
parentd99e3140a4d33e26066183ff727d8f02f56bec64 (diff)
mm: zswap: fix shrinker NULL crash with cgroup_disable=memory
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>
Diffstat (limited to 'mm')
-rw-r--r--mm/zswap.c25
1 files changed, 16 insertions, 9 deletions
diff --git a/mm/zswap.c b/mm/zswap.c
index caed028945b0..6f8850c44b61 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1331,15 +1331,22 @@ static unsigned long zswap_shrinker_count(struct shrinker *shrinker,
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 = zswap_pool_total_size >> PAGE_SHIFT;
- nr_stored = atomic_read(&zswap_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 = zswap_pool_total_size >> PAGE_SHIFT;
+ nr_stored = atomic_read(&zswap_nr_stored);
+ }
if (!nr_stored)
return 0;