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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Hao Zhang , Hao Zhang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kiryl Shutsemau (Meta)" , stable@vger.kernel.org Subject: Re: [PATCH v3] mm/huge_memory: unlock i_mmap_rwsem before releasing after-split folios Message-Id: <20260717195851.609269e143b4b9eb857f2a6a@linux-foundation.org> In-Reply-To: <20260716095424.471052-1-kirill@shutemov.name> References: <20260716095424.471052-1-kirill@shutemov.name> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 6506C1C0003 X-Stat-Signature: eqnk49g9ohyhyq7rjr1xjzfqgo4m3bqh X-HE-Tag: 1784343534-431782 X-HE-Meta: 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 C9KLDQw7 q6m4kD8c5L/rcA1H6FL29g6HEJy5WuLk5W9GA0X6TLx242B6gJiDSKFzVPVOlE45eSoMaGL8hcX7xIL2x+gRzJoCfAeSFTCmkkShJLk1XzuKot9l2oaAtuMqYEGPM0GDqYIO/e22h+cpdYqLXJn1sPRpBhQ4AeOtWlA2G7StDjt26B9nW6/2JoXk6ajsJkPyaAMwANohcPDM390K6Fp9aJXT/26NKRD8ixAfsPFhALd0g5lLi764dKc7v8riochKRKnWiRKw+rXpBOJj9/6yyy++Oirk1fc5M8FjGW+FYypXb+onBwJyG9xa+EqxD8wvUlCuomM20v0tIjMMfaD44dmwCbIbbWQU4npNjhwKgxLlkmcmM4CDdw3nVaRcHPk2/WMKEVDv8z1mFiyTZ3nc9Yqeh4nKH1oeQr2S23ZSFOJUmpLBoeusz3W8GoVq1r1PVKz+6fSmnEQGrkMM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 16 Jul 2026 10:54:24 +0100 Kiryl Shutsemau wrote: > From: "Kiryl Shutsemau (Meta)" > > __folio_split() keeps dereferencing the mapping after the split: > shmem_uncharge(mapping->host) and remap_page() while the folios are still > frozen/locked, and i_mmap_unlock_read(mapping) at the very end, after the > after-split folios have been unlocked and freed. > > Nothing holds an inode reference across that. The split relies on @folio > -- which the beyond-EOF drop loop never removes, as it starts at > folio_next(folio) -- staying locked and in the page cache to hold off > eviction. But the unlock loop unlocks @folio before i_mmap_unlock_read() > runs. If the caller's @lock_at is a tail beyond EOF, as memory_failure() > passes when splitting a poisoned tail of a shmem THP that reaches past > i_size during truncation, it too is gone from the page cache; so once > @folio is unlocked no locked, in-cache folio pins the inode, and a > concurrent final iput() can evict and RCU-free it before > i_mmap_unlock_read() touches i_mmap_rwsem: > > BUG: KASAN: slab-use-after-free in __up_read+0x634/0x790 > i_mmap_unlock_read include/linux/fs.h:537 [inline] > __folio_split+0x732/0x1640 mm/huge_memory.c:4100 > try_to_split_thp_page+0xab/0x390 mm/memory-failure.c:1675 > memory_failure+0x1394/0x26e0 mm/memory-failure.c:2470 Added as a hotfix. thanks. > mm/huge_memory.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) Sashiko might have found a pre-existing bug in there: https://sashiko.dev/#/patchset/20260716095424.471052-1-kirill@shutemov.name (why is mapping_set_update() a) a macro and b) undocumented?)