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Fri, 6 Feb 2026 16:40:39 +0900 Received: from devron.myhome.or.jp (foobar@localhost [127.0.0.1]) by devron.myhome.or.jp (8.18.2/8.18.2/Debian-1) with ESMTPS id 6167ecpq970184 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Fri, 6 Feb 2026 16:40:38 +0900 Received: (from hirofumi@localhost) by devron.myhome.or.jp (8.18.2/8.18.2/Submit) id 6167ecA5970181; Fri, 6 Feb 2026 16:40:38 +0900 From: OGAWA Hirofumi To: syzbot Cc: linkinjeon@kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, sj1557.seo@samsung.com, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [exfat?] KCSAN: data-race in fat12_ent_put / fat_mirror_bhs In-Reply-To: <69858d8b.050a0220.3b3015.0031.GAE@google.com> References: <69858d8b.050a0220.3b3015.0031.GAE@google.com> Date: Fri, 06 Feb 2026 16:40:38 +0900 Message-ID: <87h5rue2vd.fsf@mail.parknet.co.jp> User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain syzbot writes: > Hello, > > syzbot found the following issue on: > > HEAD commit: de0674d9bc69 Merge tag 'for-6.19-rc8-tag' of git://git.ker.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=15f240aa580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=8e27f4588a0f2183 > dashboard link: https://syzkaller.appspot.com/bug?extid=51b4c65bb770155d058f > compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8 > > Unfortunately, I don't have any reproducer for this issue yet. > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/bfedab2f6279/disk-de0674d9.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/f012a4cb8d82/vmlinux-de0674d9.xz > kernel image: https://storage.googleapis.com/syzbot-assets/acb727c49110/bzImage-de0674d9.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+51b4c65bb770155d058f@syzkaller.appspotmail.com This looks like same with the following thread. https://lore.kernel.org/all/20250902081727.7146-1-anmuxixixi@gmail.com/ And this temporary inconsistency will be fixed until unmount, so it should be no corruption by this race. Let me know if corruption remained after unmount. Thanks. > ================================================================== > BUG: KCSAN: data-race in fat12_ent_put / fat_mirror_bhs > > read-write to 0xffff888129151032 of 1 bytes by task 4937 on cpu 1: > fat12_ent_put+0xc4/0x170 fs/fat/fatent.c:165 > fat_ent_write+0x6c/0xe0 fs/fat/fatent.c:417 > fat_chain_add+0x16c/0x490 fs/fat/misc.c:136 > fat_add_cluster fs/fat/inode.c:113 [inline] > __fat_get_block fs/fat/inode.c:155 [inline] > fat_get_block+0x46c/0x5e0 fs/fat/inode.c:190 > __block_write_begin_int+0x400/0xf90 fs/buffer.c:2145 > block_write_begin fs/buffer.c:2256 [inline] > cont_write_begin+0x5fe/0x970 fs/buffer.c:2594 > fat_write_begin+0x4f/0xe0 fs/fat/inode.c:230 > generic_perform_write+0x183/0x490 mm/filemap.c:4314 > __generic_file_write_iter+0x9e/0x120 mm/filemap.c:4431 > generic_file_write_iter+0x8d/0x310 mm/filemap.c:4457 > new_sync_write fs/read_write.c:593 [inline] > vfs_write+0x5a6/0x9f0 fs/read_write.c:686 > ksys_write+0xdc/0x1a0 fs/read_write.c:738 > __do_sys_write fs/read_write.c:749 [inline] > __se_sys_write fs/read_write.c:746 [inline] > __x64_sys_write+0x40/0x50 fs/read_write.c:746 > x64_sys_call+0x2847/0x3000 arch/x86/include/generated/asm/syscalls_64.h:2 > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > read to 0xffff888129151000 of 512 bytes by task 4940 on cpu 0: > fat_mirror_bhs+0x1df/0x320 fs/fat/fatent.c:395 > fat_alloc_clusters+0xb48/0xc50 fs/fat/fatent.c:543 > fat_add_cluster fs/fat/inode.c:108 [inline] > __fat_get_block fs/fat/inode.c:155 [inline] > fat_get_block+0x258/0x5e0 fs/fat/inode.c:190 > __block_write_begin_int+0x400/0xf90 fs/buffer.c:2145 > block_write_begin fs/buffer.c:2256 [inline] > cont_write_begin+0x5fe/0x970 fs/buffer.c:2594 > fat_write_begin+0x4f/0xe0 fs/fat/inode.c:230 > generic_perform_write+0x183/0x490 mm/filemap.c:4314 > __generic_file_write_iter+0x9e/0x120 mm/filemap.c:4431 > generic_file_write_iter+0x8d/0x310 mm/filemap.c:4457 > __kernel_write_iter+0x319/0x590 fs/read_write.c:619 > dump_emit_page fs/coredump.c:1298 [inline] > dump_user_range+0xa7d/0xdb0 fs/coredump.c:1372 > elf_core_dump+0x21a2/0x2330 fs/binfmt_elf.c:2111 > coredump_write+0xacf/0xdf0 fs/coredump.c:1049 > do_coredump fs/coredump.c:1126 [inline] > vfs_coredump+0x26bc/0x3120 fs/coredump.c:1200 > get_signal+0xd7b/0xf60 kernel/signal.c:3019 > arch_do_signal_or_restart+0x96/0x450 arch/x86/kernel/signal.c:337 > __exit_to_user_mode_loop kernel/entry/common.c:41 [inline] > exit_to_user_mode_loop kernel/entry/common.c:75 [inline] > __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline] > irqentry_exit_to_user_mode_prepare include/linux/irq-entry-common.h:270 [inline] > irqentry_exit_to_user_mode include/linux/irq-entry-common.h:339 [inline] > irqentry_exit+0xf7/0x510 kernel/entry/common.c:196 > asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618 > > Reported by Kernel Concurrency Sanitizer on: > CPU: 0 UID: 0 PID: 4940 Comm: syz.3.398 Not tainted syzkaller #0 PREEMPT(voluntary) > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 > ================================================================== > syz.3.398 (4940) used greatest stack depth: 8696 bytes left > > > --- > This report is generated by a bot. It may contain errors. > See https://goo.gl/tpsmEJ for more information about syzbot. > syzbot engineers can be reached at syzkaller@googlegroups.com. > > syzbot will keep track of this issue. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > > If the report is already addressed, let syzbot know by replying with: > #syz fix: exact-commit-title > > If you want to overwrite report's subsystems, reply with: > #syz set subsystems: new-subsystem > (See the list of subsystem names on the web dashboard) > > If the report is a duplicate of another one, reply with: > #syz dup: exact-subject-of-another-report > > If you want to undo deduplication, reply with: > #syz undup -- OGAWA Hirofumi