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charset=us-ascii Content-Disposition: inline In-Reply-To: <568c10e8-c225-b3c4-483a-5bb3329de4c5@huawei.com> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 525D8120015 X-Stat-Signature: ad3x93fipsaem43iip4oofkw5au5f1ru X-HE-Tag: 1675068527-258549 X-HE-Meta: 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 T7IYwLfe PleG3ZWOHI3nM3Foi7nxm7hzjnseARbj6zbmUb8m5SoR+gjypdxpVhrR/44Efs18J/lYqLqU3tBbcEyeFnoGN0dZp1KaXoAb1CYdNbVfO+QvoSzEC3KCvbUYr65hOa/ZbqU7Olzas7ZeL624xNFZWiB18a8YvQe5Z+Ly4zA/9uNFa4eZJW+djolkkIteWdL8R2tSjcAXaOYW6pAjovNYmmj82V2UmUXHr0z+iRQaePq6RXD0= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon 30-01-23 09:16:13, Kefeng Wang wrote: > > > On 2023/1/30 5:48, Andrew Morton wrote: > > On Sun, 29 Jan 2023 10:44:51 +0800 Kefeng Wang wrote: > > > > > As commit 18365225f044 ("hwpoison, memcg: forcibly uncharge LRU pages"), > > > > Merged in 2017. > > > > > 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() to > > > fix it. > > > > > > Reported-by: Ma Wupeng > > > Fixes: 97b27821b485 ("writeback, memcg: Implement foreign dirty flushing") > > > > Merged in 2019. > > > > > --- 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); > > > } > > > > Has this null deref actually been observed, or is this from code > > inspection? (This is why it's nice to include the Link: after a > > Reported-by!) > > It does occurs in our internal test and report by wupeng(based v5.10), > > BUG: KASAN: user-memory-access in > mem_cgroup_track_foreign_dirty_slowpath+0xc0/0x480 mm/memcontrol.c:4708 > Read of size 8 at addr 0000000000001000 by task syz-executor.2/28325 > > CPU: 2 PID: 28325 Comm: syz-executor.2 Tainted: G W > 5.10.0-03333-g48e46a146cbc-dirty #1 > Hardware name: linux,dummy-virt (DT) > Call trace: > ... > mem_cgroup_track_foreign_dirty_slowpath+0xc0/0x480 mm/memcontrol.c:4708 > mem_cgroup_track_foreign_dirty include/linux/memcontrol.h:1880 [inline] > account_page_dirtied+0x9a0/0xa90 mm/page-writeback.c:2436 > __set_page_dirty+0x1f8/0x4b0 fs/buffer.c:608 > __set_page_dirty_buffers+0x3d0/0x550 fs/buffer.c:668 > set_page_dirty+0x158/0x500 mm/page-writeback.c:2575 > filemap_page_mkwrite+0x3dc/0x490 mm/filemap.c:3224 > do_page_mkwrite+0xc4/0x3d0 mm/memory.c:2786 > wp_page_shared+0x14c/0x980 mm/memory.c:3118 > do_wp_page+0x930/0xbc0 mm/memory.c:3219 > handle_pte_fault+0x5e0/0x630 mm/memory.c:4570 > __handle_mm_fault+0x41c/0x910 mm/memory.c:4690 > handle_mm_fault+0x25c/0x484 mm/memory.c:4788 > __do_page_fault arch/arm64/mm/fault.c:440 [inline] > do_page_fault+0x3ac/0x9d4 arch/arm64/mm/fault.c:539 Just to make sure I understand. The page has been hwpoisoned, uncharged but stayed in the page cache so a next page fault on the address has blowned up? Say we address the NULL memcg case. What is the resulting behavior? Doesn't userspace access a poisoned page and get a silend memory corruption? -- Michal Hocko SUSE Labs