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s=arc-20220608; d=hostedemail.com; t=1764148490; a=rsa-sha256; cv=none; b=xNtDKLzALN05ixwm48XRjRAlmZYWgBd0/zTeQhQKXc46nF5mj2AjdUeg1/kFdZNqZI/Q8w Yeh2SuAqKmBTzDPEACEF11i6yLxsI9MaFrk4jqRmuPMVNeh5wuQ21QmQRHKPDzVsXenWnw nibGqy5xsbUu0PnJzawcu9YMhheH2qM= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=none; spf=none (imf24.hostedemail.com: domain of wozizhi@huaweicloud.com has no SPF policy when checking 45.249.212.51) smtp.mailfrom=wozizhi@huaweicloud.com; dmarc=none Received: from mail.maildlp.com (unknown [172.19.163.216]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTPS id 4dGYlN4878zYQvKy for ; Wed, 26 Nov 2025 17:13:52 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id 3CE651A1E71 for ; Wed, 26 Nov 2025 17:14:44 +0800 (CST) Received: from huaweicloud.com (unknown [10.50.87.129]) by APP4 (Coremail) with SMTP id gCh0CgAXQV4DxSZpUsJHCA--.59425S4; Wed, 26 Nov 2025 17:14:44 +0800 (CST) From: Zizhi Wo To: jack@suse.com, brauner@kernel.org, hch@lst.de, akpm@linux-foundation.org, linux@armlinux.org.uk Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, wozizhi@huawei.com, yangerkun@huawei.com, wangkefeng.wang@huawei.com, pangliyuan1@huawei.com, xieyuanbin1@huawei.com Subject: [Bug report] hash_name() may cross page boundary and trigger sleep in RCU context Date: Wed, 26 Nov 2025 17:05:05 +0800 Message-Id: <20251126090505.3057219-1-wozizhi@huaweicloud.com> X-Mailer: git-send-email 2.39.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CM-TRANSID:gCh0CgAXQV4DxSZpUsJHCA--.59425S4 X-Coremail-Antispam: 1UD129KBjvJXoW7tFW7Jr45Ww1xtF1rury5XFb_yoW5JFWrpr 45CryYkrZxZryrZr10ka9IgFyYyayUGr43Grs2qryUua1agF1avF48ta4Y9r9Iqr1DWa9r Wrs09wn7uw1q9FUanT9S1TB71UUUUUDqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUvab4IE77IF4wAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_tr0E3s1l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x 0267AKxVW0oVCq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG 6I80ewAv7VC0I7IYx2IY67AKxVWUAVWUtwAv7VC2z280aVAFwI0_Gr1j6F4UJwAm72CE4I kC6x0Yz7v_Jr0_Gr1lF7xvr2IYc2Ij64vIr41lFIxGxcIEc7CjxVA2Y2ka0xkIwI1lc7Cj xVAaw2AFwI0_Jw0_GFyl42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2 IqxVAqx4xG67AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v2 6r1q6r43MIIYrxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2 IY6xkF7I0E14v26r4j6F4UMIIF0xvE42xK8VAvwI8IcIk0rVWUJVWUCwCI42IY6I8E87Iv 67AKxVWUJVW8JwCI42IY6I8E87Iv6xkF7I0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyT uYvjxUoEfOUUUUU X-CM-SenderInfo: pzr2x6tkl6x35dzhxuhorxvhhfrp/ X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 8AF9918000C X-Stat-Signature: 9dc4pn1938tcxiym3cwf95zkwebexs76 X-HE-Tag: 1764148489-713200 X-HE-Meta: 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 boCcX9Uv rvHj/Ku7EJXsKA1p4fKzxC48DeS3BmQCQsf244yhfDA/vj0vwCA2Y5hzNnWARuVwDwUd9b7ExiulB2R3K/rq+aMluGzxYTdYJtpzkjFos8HfKrsIKswvqKoc1Ra7jIoGP9JSeIMbrSaooIG5hyO5nhqbATngMY4gUVobJXKSP54PQ1Lhg8VzjWZ5Wqdkomx3BMTzUOKfHTh8ws85gHiLwvrwvng== 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: List-Subscribe: List-Unsubscribe: We're running into the following issue on an ARM32 platform with the linux 5.10 kernel: [] (__dabt_svc) from [] (link_path_walk.part.7+0x108/0x45c) [] (link_path_walk.part.7) from [] (path_openat+0xc4/0x10ec) [] (path_openat) from [] (do_filp_open+0x9c/0x114) [] (do_filp_open) from [] (do_sys_openat2+0x418/0x528) [] (do_sys_openat2) from [] (do_sys_open+0x88/0xe4) [] (do_sys_open) from [] (ret_fast_syscall+0x0/0x58) ... [] (unwind_backtrace) from [] (show_stack+0x20/0x24) [] (show_stack) from [] (dump_stack+0xd8/0xf8) [] (dump_stack) from [] (___might_sleep+0x19c/0x1e4) [] (___might_sleep) from [] (do_page_fault+0x2f8/0x51c) [] (do_page_fault) from [] (do_DataAbort+0x90/0x118) [] (do_DataAbort) from [] (__dabt_svc+0x58/0x80) ... During the execution of hash_name()->load_unaligned_zeropad(), a potential memory access beyond the PAGE boundary may occur. For example, when the filename length is near the PAGE_SIZE boundary. This triggers a page fault, which leads to a call to do_page_fault()->mmap_read_trylock(). If we can't acquire the lock, we have to fall back to the mmap_read_lock() path, which calls might_sleep(). This breaks RCU semantics because path lookup occurs under an RCU read-side critical section. In linux-mainline, arm/arm64 do_page_fault() still has this problem: lock_mm_and_find_vma->get_mmap_lock_carefully->mmap_read_lock_killable. And before commit bfcfaa77bdf0 ("vfs: use 'unsigned long' accesses for dcache name comparison and hashing"), hash_name accessed the name byte by byte. To prevent load_unaligned_zeropad() from accessing beyond the valid memory region, we would need to intercept such cases beforehand? But doing so would require replicating the internal logic of load_unaligned_zeropad(), including handling endianness and constructing the correct value manually. Given that load_unaligned_zeropad() is used in many places across the kernel, we currently haven't found a good solution to address this cleanly. What would be the recommended way to handle this situation? Would appreciate any feedback and guidance from the community. Thanks!