+ mm-memcg-fix-null-pointer-in-mem_cgroup_track_foreign_dirty_slowpath.patch added to mm-hotfixes-unstable branch

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

The patch titled
     Subject: mm: memcg: fix NULL pointer in mem_cgroup_track_foreign_dirty_slowpath()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-memcg-fix-null-pointer-in-mem_cgroup_track_foreign_dirty_slowpath.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memcg-fix-null-pointer-in-mem_cgroup_track_foreign_dirty_slowpath.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: Kefeng Wang <wangkefeng.wang@huawei.com>
Subject: mm: memcg: fix NULL pointer in mem_cgroup_track_foreign_dirty_slowpath()
Date: Sun, 29 Jan 2023 12:09:45 +0800

As commit 18365225f044 ("hwpoison, memcg: forcibly uncharge LRU pages"),
hwpoison will forcibly uncharg a LRU hwpoisoned page, the folio_memcg
could be NULl, then, mem_cgroup_track_foreign_dirty_slowpath() could
occurs a NULL pointer dereference, let's do not record the foreign
writebacks for folio memcg is null in mem_cgroup_track_foreign_dirty() to
fix it.

Link: https://lkml.kernel.org/r/20230129040945.180629-1-wangkefeng.wang@huawei.com
Fixes: 97b27821b485 ("writeback, memcg: Implement foreign dirty flushing")
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reported-by: Ma Wupeng <mawupeng1@huawei.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Ma Wupeng <mawupeng1@huawei.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/include/linux/memcontrol.h~mm-memcg-fix-null-pointer-in-mem_cgroup_track_foreign_dirty_slowpath
+++ a/include/linux/memcontrol.h
@@ -1666,10 +1666,13 @@ void mem_cgroup_track_foreign_dirty_slow
 static inline void mem_cgroup_track_foreign_dirty(struct folio *folio,
 						  struct bdi_writeback *wb)
 {
+	struct mem_cgroup *memcg;
+
 	if (mem_cgroup_disabled())
 		return;
 
-	if (unlikely(&folio_memcg(folio)->css != wb->memcg_css))
+	memcg = folio_memcg(folio);
+	if (unlikely(memcg && &memcg->css != wb->memcg_css))
 		mem_cgroup_track_foreign_dirty_slowpath(folio, wb);
 }
 
_

Patches currently in -mm which might be from wangkefeng.wang@huawei.com are

mm-hwposion-support-recovery-from-ksm_might_need_to_copy.patch
mm-hwposion-support-recovery-from-ksm_might_need_to_copy-v3.patch
mm-memcg-fix-null-pointer-in-mem_cgroup_track_foreign_dirty_slowpath.patch
mm-madvise-use-vm_normal_folio-in-madvise_free_pte_range.patch