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author | Johannes Weiner <hannes@cmpxchg.org> | 2024-04-18 15:26:28 +0300 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2024-05-02 17:35:32 +0300 |
commit | b0fdabc908a7f81d12382c87ca9e46a9c2e14042 (patch) | |
tree | 108dd3f5b0aaf04a7d7da97bb918517b68e74c77 | |
parent | 9fdcc5b6359dfdaa52a55033bf50e2cedd66eb32 (diff) | |
download | linux-b0fdabc908a7f81d12382c87ca9e46a9c2e14042.tar.xz |
mm: zswap: fix shrinker NULL crash with cgroup_disable=memory
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@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>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r-- | mm/zswap.c | 25 |
1 files changed, 16 insertions, 9 deletions
diff --git a/mm/zswap.c b/mm/zswap.c index e9c04387195f..69766f2c5a6c 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -653,15 +653,22 @@ 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 = 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; |