+ null-pointer-dereference-while-shrinking-zswap.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: Re: Null pointer dereference while shrinking zswap
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     null-pointer-dereference-while-shrinking-zswap.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/null-pointer-dereference-while-shrinking-zswap.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: Null pointer dereference while shrinking zswap
Date: Wed, 17 Apr 2024 10:33:24 -0400

temp version of this fix, for testing

Link: https://lkml.kernel.org/r/20240417143324.GA1055428@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Tested-by: Richard W.M. Jones <rjones@redhat.com>
Tested-By: Christian Heusel <christian@heusel.eu>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/zswap.c |   25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

--- a/mm/zswap.c~null-pointer-dereference-while-shrinking-zswap
+++ a/mm/zswap.c
@@ -1331,15 +1331,22 @@ 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 = 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;
_

Patches currently in -mm which might be from hannes@cmpxchg.org are

null-pointer-dereference-while-shrinking-zswap.patch
mm-zswap-optimize-zswap-pool-size-tracking.patch
mm-zpool-return-pool-size-in-pages.patch
mm-page_alloc-remove-pcppage-migratetype-caching.patch
mm-page_alloc-optimize-free_unref_folios.patch
mm-page_alloc-fix-up-block-types-when-merging-compatible-blocks.patch
mm-page_alloc-move-free-pages-when-converting-block-during-isolation.patch
mm-page_alloc-fix-move_freepages_block-range-error.patch
mm-page_alloc-fix-freelist-movement-during-block-conversion.patch
mm-page_alloc-close-migratetype-race-between-freeing-and-stealing.patch
mm-page_isolation-prepare-for-hygienic-freelists.patch
mm-page_isolation-prepare-for-hygienic-freelists-fix.patch
mm-page_alloc-consolidate-free-page-accounting.patch
mm-page_alloc-consolidate-free-page-accounting-fix.patch
mm-page_alloc-consolidate-free-page-accounting-fix-2.patch
mm-page_alloc-batch-vmstat-updates-in-expand.patch