The patch below does not apply to the 6.8-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.8.y git checkout FETCH_HEAD git cherry-pick -x 682886ec69d22363819a83ddddd5d66cb5c791e1 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024042923-monday-hamlet-26ca@gregkh' --subject-prefix 'PATCH 6.8.y' HEAD^..

Possible dependencies:

682886ec69d2 ("mm: zswap: fix shrinker NULL crash with cgroup_disable=memory") 30fb6a8d9e33 ("mm: zswap: fix writeback shinker GFP_NOIO/GFP_NOFS recursion") e35606e4167d ("mm/zswap: global lru and shrinker shared by all zswap_pools fix") bf9b7df23cb3 ("mm/zswap: global lru and shrinker shared by all zswap_pools") 5182661a11ba ("mm: zswap: function ordering: move entry sections out of LRU section") 506a86c5e221 ("mm: zswap: function ordering: public lru api") abca07c04aa5 ("mm: zswap: function ordering: pool params") c1a0ecb82bdc ("mm: zswap: function ordering: zswap_pools") 39f3ec8eaa60 ("mm: zswap: function ordering: pool refcounting") a984649b5c1f ("mm: zswap: function ordering: pool alloc & free") be7fc97c5283 ("mm: zswap: further cleanup zswap_store()") fa9ad6e21003 ("mm: zswap: break out zwap_compress()") ff2972aa1b5d ("mm: zswap: rename __zswap_load() to zswap_decompress()") 7dd1f7f0fc1c ("mm: zswap: move zswap_invalidate_entry() to related functions") 5b297f70bb26 ("mm: zswap: inline and remove zswap_entry_find_get()") 5878303c5353 ("mm/zswap: fix race between lru writeback and swapoff") db128f5fdee9 ("mm: zswap: remove unused tree argument in zswap_entry_put()") 44c7c734a513 ("mm/zswap: split zswap rb-tree") bb29fd7760ae ("mm/zswap: make sure each swapfile always have zswap rb-tree") 8409a385a6b4 ("mm/zswap: improve with alloc_workqueue() call")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 682886ec69d22363819a83ddddd5d66cb5c791e1 Mon Sep 17 00:00:00 2001 From: Johannes Weiner hannes@cmpxchg.org Date: Thu, 18 Apr 2024 08:26:28 -0400 Subject: [PATCH] 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

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;