From:   Kefeng Wang <wangkefeng.wang@huawei.com>
To:     Andrew Morton <akpm@linux-foundation.org>
CC:     Tejun Heo <tj@kernel.org>, Jens Axboe <axboe@kernel.dk>,
        Jan Kara <jack@suse.cz>, Shakeel Butt <shakeelb@google.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Ma Wupeng <mawupeng1@huawei.com>
Subject: [PATCH resend] mm: memcg: fix NULL pointer in mem_cgroup_track_foreign_dirty_slowpath()
Date:   Sun, 29 Jan 2023 12:09:45 +0800
Message-ID: <20230129040945.180629-1-wangkefeng.wang@huawei.com>
In-Reply-To: <20230129024451.121590-1-wangkefeng.wang@huawei.com>
References: <20230129024451.121590-1-wangkefeng.wang@huawei.com>
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Precedence: bulk

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.

Reported-by: Ma Wupeng <mawupeng1@huawei.com>
Fixes: 97b27821b485 ("writeback, memcg: Implement foreign dirty flushing")
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
resend: correct function name
 include/linux/memcontrol.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index eb6e5b18e1ad..35478695cabf 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1688,10 +1688,13 @@ void mem_cgroup_track_foreign_dirty_slowpath(struct folio *folio,
 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);
 }
 
-- 
2.35.3