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Message-ID: <CAKFNMonPU4PhL6_GAbiXBbOB7vc313JQvw06HgZ_a_t0_OhgbQ@mail.gmail.com>
Date: Fri, 9 May 2025 01:37:11 +0900
From: Ryusuke Konishi <konishi.ryusuke@...il.com>
To: syzbot <syzbot+81394db39b0e2ed2db06@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org, linux-nilfs@...r.kernel.org,
syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [nilfs?] possible deadlock in nilfs_segctor_construct
On Fri, May 9, 2025 at 1:22 AM syzbot
<syzbot+81394db39b0e2ed2db06@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: e8ab83e34bdc Merge tag 'arm64-fixes' of git://git.kernel.o..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=146e70f4580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=a9a25b7a36123454
> dashboard link: https://syzkaller.appspot.com/bug?extid=81394db39b0e2ed2db06
> compiler: Debian clang version 20.1.2 (++20250402124445+58df0ef89dd6-1~exp1~20250402004600.97), Debian LLD 20.1.2
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=148c9a70580000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1530b8d4580000
>
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-e8ab83e3.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/b26f15c51ac7/vmlinux-e8ab83e3.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/05e91bf788d8/bzImage-e8ab83e3.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/09efd3b532ea/mount_0.gz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+81394db39b0e2ed2db06@...kaller.appspotmail.com
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 6.15.0-rc4-syzkaller-00296-ge8ab83e34bdc #0 Not tainted
> ------------------------------------------------------
> segctord/5299 is trying to acquire lock:
> ffff88801189e090 (&nilfs->ns_sem){++++}-{4:4}, at: nilfs_segctor_construct+0x2b1/0x690 fs/nilfs2/segment.c:2485
>
> but task is already holding lock:
> ffff88801189e2a0 (&nilfs->ns_segctor_sem){++++}-{4:4}, at: nilfs_transaction_lock+0x253/0x4c0 fs/nilfs2/segment.c:357
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #5 (&nilfs->ns_segctor_sem){++++}-{4:4}:
> lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
> down_read+0x46/0x2e0 kernel/locking/rwsem.c:1524
> nilfs_transaction_begin+0x365/0x710 fs/nilfs2/segment.c:221
> nilfs_create+0xc9/0x2f0 fs/nilfs2/namei.c:95
> lookup_open fs/namei.c:3701 [inline]
> open_last_lookups fs/namei.c:3800 [inline]
> path_openat+0x14f1/0x3830 fs/namei.c:4036
> do_filp_open+0x1fa/0x410 fs/namei.c:4066
> do_sys_openat2+0x121/0x1c0 fs/open.c:1429
> do_sys_open fs/open.c:1444 [inline]
> __do_sys_openat fs/open.c:1460 [inline]
> __se_sys_openat fs/open.c:1455 [inline]
> __x64_sys_openat+0x138/0x170 fs/open.c:1455
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> -> #4 (sb_internal#2){.+.+}-{0:0}:
> lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
> percpu_down_read include/linux/percpu-rwsem.h:52 [inline]
> __sb_start_write include/linux/fs.h:1783 [inline]
> sb_start_intwrite include/linux/fs.h:1966 [inline]
> nilfs_transaction_begin+0x268/0x710 fs/nilfs2/segment.c:218
> nilfs_page_mkwrite+0x8b0/0xc20 fs/nilfs2/file.c:95
> do_page_mkwrite+0x14a/0x310 mm/memory.c:3287
> do_shared_fault mm/memory.c:5594 [inline]
> do_fault mm/memory.c:5656 [inline]
> do_pte_missing mm/memory.c:4160 [inline]
> handle_pte_fault mm/memory.c:5997 [inline]
> __handle_mm_fault+0x18d2/0x5380 mm/memory.c:6140
> handle_mm_fault+0x3f6/0x8c0 mm/memory.c:6309
> do_user_addr_fault+0x764/0x1390 arch/x86/mm/fault.c:1388
> handle_page_fault arch/x86/mm/fault.c:1480 [inline]
> exc_page_fault+0x68/0x110 arch/x86/mm/fault.c:1538
> asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
>
> -> #3 (sb_pagefaults){.+.+}-{0:0}:
> lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
> percpu_down_read include/linux/percpu-rwsem.h:52 [inline]
> __sb_start_write include/linux/fs.h:1783 [inline]
> sb_start_pagefault include/linux/fs.h:1948 [inline]
> nilfs_page_mkwrite+0x21e/0xc20 fs/nilfs2/file.c:57
> do_page_mkwrite+0x14a/0x310 mm/memory.c:3287
> do_shared_fault mm/memory.c:5594 [inline]
> do_fault mm/memory.c:5656 [inline]
> do_pte_missing mm/memory.c:4160 [inline]
> handle_pte_fault mm/memory.c:5997 [inline]
> __handle_mm_fault+0x18d2/0x5380 mm/memory.c:6140
> handle_mm_fault+0x3f6/0x8c0 mm/memory.c:6309
> do_user_addr_fault+0x764/0x1390 arch/x86/mm/fault.c:1388
> handle_page_fault arch/x86/mm/fault.c:1480 [inline]
> exc_page_fault+0x68/0x110 arch/x86/mm/fault.c:1538
> asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
>
> -> #2 (&mm->mmap_lock){++++}-{4:4}:
> lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
> __might_fault+0xcc/0x130 mm/memory.c:7151
> _copy_to_iter+0xf3/0x15a0 lib/iov_iter.c:184
> copy_page_to_iter+0xa7/0x150 lib/iov_iter.c:362
> copy_folio_to_iter include/linux/uio.h:198 [inline]
> filemap_read+0x78d/0x11d0 mm/filemap.c:2753
> blkdev_read_iter+0x30a/0x440 block/fops.c:809
> new_sync_read fs/read_write.c:489 [inline]
> vfs_read+0x4cd/0x980 fs/read_write.c:570
> ksys_read+0x145/0x250 fs/read_write.c:713
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> -> #1 (&sb->s_type->i_mutex_key#8){++++}-{4:4}:
> lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
> down_write+0x96/0x1f0 kernel/locking/rwsem.c:1577
> inode_lock include/linux/fs.h:867 [inline]
> set_blocksize+0x23b/0x500 block/bdev.c:203
> sb_set_blocksize block/bdev.c:224 [inline]
> sb_min_blocksize+0x119/0x210 block/bdev.c:239
> init_nilfs+0x43/0x690 fs/nilfs2/the_nilfs.c:710
> nilfs_fill_super+0x8f/0x650 fs/nilfs2/super.c:1060
> nilfs_get_tree+0x4f4/0x870 fs/nilfs2/super.c:1228
> vfs_get_tree+0x8f/0x2b0 fs/super.c:1759
> do_new_mount+0x24a/0xa40 fs/namespace.c:3884
> do_mount fs/namespace.c:4224 [inline]
> __do_sys_mount fs/namespace.c:4435 [inline]
> __se_sys_mount+0x317/0x410 fs/namespace.c:4412
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> -> #0 (&nilfs->ns_sem){++++}-{4:4}:
> check_prev_add kernel/locking/lockdep.c:3166 [inline]
> check_prevs_add kernel/locking/lockdep.c:3285 [inline]
> validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3909
> __lock_acquire+0xaac/0xd20 kernel/locking/lockdep.c:5235
> lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
> down_write+0x96/0x1f0 kernel/locking/rwsem.c:1577
> nilfs_segctor_construct+0x2b1/0x690 fs/nilfs2/segment.c:2485
> nilfs_segctor_thread_construct fs/nilfs2/segment.c:2586 [inline]
> nilfs_segctor_thread+0x6f7/0xe00 fs/nilfs2/segment.c:2700
> kthread+0x70e/0x8a0 kernel/kthread.c:464
> ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>
> other info that might help us debug this:
>
> Chain exists of:
> &nilfs->ns_sem --> sb_internal#2 --> &nilfs->ns_segctor_sem
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&nilfs->ns_segctor_sem);
> lock(sb_internal#2);
> lock(&nilfs->ns_segctor_sem);
> lock(&nilfs->ns_sem);
>
> *** DEADLOCK ***
>
> 1 lock held by segctord/5299:
> #0: ffff88801189e2a0 (&nilfs->ns_segctor_sem){++++}-{4:4}, at: nilfs_transaction_lock+0x253/0x4c0 fs/nilfs2/segment.c:357
>
> stack backtrace:
> CPU: 0 UID: 0 PID: 5299 Comm: segctord Not tainted 6.15.0-rc4-syzkaller-00296-ge8ab83e34bdc #0 PREEMPT(full)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> Call Trace:
> <TASK>
> dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
> print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2079
> check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2211
> check_prev_add kernel/locking/lockdep.c:3166 [inline]
> check_prevs_add kernel/locking/lockdep.c:3285 [inline]
> validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3909
> __lock_acquire+0xaac/0xd20 kernel/locking/lockdep.c:5235
> lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
> down_write+0x96/0x1f0 kernel/locking/rwsem.c:1577
> nilfs_segctor_construct+0x2b1/0x690 fs/nilfs2/segment.c:2485
> nilfs_segctor_thread_construct fs/nilfs2/segment.c:2586 [inline]
> nilfs_segctor_thread+0x6f7/0xe00 fs/nilfs2/segment.c:2700
> kthread+0x70e/0x8a0 kernel/kthread.c:464
> ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
> </TASK>
>
>
> ---
> 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@...glegroups.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 syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.
>
> 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
This looks a false positive deadlock warning similar to the one in the
syzbot report
below, caused by inode locking introduced in set_blocksize():
#syz dup: possible deadlock in __nilfs_error (3)
A patch to fix this warning is already on its way to the mainline.
Ryusuke Konishi
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