From: syzbot <syzbot+5c01398781fb51df783a@syzkaller.appspotmail.com>
To: clm@fb.com, dsterba@suse.com, linux-btrfs@vger.kernel.org,
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com
Subject: [syzbot] [btrfs?] possible deadlock in set_blocksize
Date: Sat, 24 Oct 2026 06:33:50 -0700 [thread overview]
Message-ID: <6adcb3be.4ce6c07b.2dfc0c.0005.GAE@google.com> (raw)
Hello,
syzbot found the following issue on:
HEAD commit: 4169c9c90532 powerpc/irq: Fix build with CONFIG_PROC_FS=n
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=14fdcbcd580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e397d1e24d3cb03
dashboard link: https://syzkaller.appspot.com/bug?extid=5c01398781fb51df783a
compiler: Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=132c1a31580000
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5c01398781fb51df783a@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz-executor324/6058 is trying to acquire lock:
ffff888024d4e3e8 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
ffff888024d4e3e8 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: set_blocksize+0x1e6/0x440 block/bdev.c:202
but task is already holding lock:
ffff888027eb26a8 (btrfs_trans_num_extwriters){.+.+}-{0:0}, at: join_transaction+0x6b2/0xd40 fs/btrfs/transaction.c:331
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #3 (btrfs_trans_num_extwriters){.+.+}-{0:0}:
join_transaction+0x18a/0xd40 fs/btrfs/transaction.c:356
start_transaction+0x731/0x1830 fs/btrfs/transaction.c:770
btrfs_create_common+0x15c/0x310 fs/btrfs/inode.c:6991
lookup_open+0xedc/0x1970 fs/namei.c:4569
open_last_lookups fs/namei.c:4768 [inline]
path_openat+0x70c/0x20f0 fs/namei.c:5007
do_file_open+0x23e/0x4a0 fs/namei.c:5039
do_sys_openat2+0x115/0x200 fs/open.c:1442
do_sys_open fs/open.c:1448 [inline]
__do_sys_openat fs/open.c:1464 [inline]
__se_sys_openat fs/open.c:1459 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1459
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #2 (btrfs_trans_num_writers){.+.+}-{0:0}:
__lock_release kernel/locking/lockdep.c:5627 [inline]
lock_release+0x1a3/0x3c0 kernel/locking/lockdep.c:5964
percpu_up_read include/linux/percpu-rwsem.h:114 [inline]
__sb_end_write include/linux/fs/super.h:14 [inline]
sb_end_intwrite+0x26/0x190 include/linux/fs/super.h:101
__btrfs_end_transaction+0x237/0x640 fs/btrfs/transaction.c:1147
btrfs_dirty_inode+0x14c/0x190 fs/btrfs/inode.c:6444
touch_atime+0x2f8/0x670 fs/inode.c:2325
file_accessed include/linux/fs.h:2279 [inline]
btrfs_file_mmap_prepare+0x172/0x1f0 fs/btrfs/file.c:2003
vfs_mmap_prepare include/linux/fs.h:2071 [inline]
call_mmap_prepare mm/vma.c:2815 [inline]
__mmap_region mm/vma.c:2913 [inline]
mmap_region+0xe88/0x23c0 mm/vma.c:3014
do_mmap+0xe0a/0x1300 mm/mmap.c:573
vm_mmap_pgoff+0x272/0x4e0 mm/util.c:581
ksys_mmap_pgoff+0x4dc/0x760 mm/mmap.c:619
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #1 (&mm->mmap_lock){++++}-{4:4}:
__might_fault+0xcb/0x130 mm/memory.c:7419
_copy_to_iter+0xf9/0x1810 lib/iov_iter.c:196
copy_page_to_iter+0x23f/0x330 lib/iov_iter.c:374
copy_folio_to_iter include/linux/uio.h:204 [inline]
filemap_read+0x7af/0x11e0 mm/filemap.c:2893
blkdev_read_iter+0x2f1/0x420 block/fops.c:838
new_sync_read fs/read_write.c:493 [inline]
vfs_read+0x595/0xa80 fs/read_write.c:574
ksys_read+0x150/0x270 fs/read_write.c:716
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #0 (&sb->s_type->i_mutex_key#10){++++}-{4:4}:
check_prev_add kernel/locking/lockdep.c:3209 [inline]
check_prevs_add kernel/locking/lockdep.c:3328 [inline]
validate_chain kernel/locking/lockdep.c:3952 [inline]
__lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
down_write+0x91/0x200 kernel/locking/rwsem.c:1631
inode_lock include/linux/fs.h:1024 [inline]
set_blocksize+0x1e6/0x440 block/bdev.c:202
btrfs_init_new_device+0xa4e/0x1cf0 fs/btrfs/volumes.c:3046
btrfs_ioctl_add_dev+0x1ad/0x640 fs/btrfs/ioctl.c:2571
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
other info that might help us debug this:
Chain exists of:
&sb->s_type->i_mutex_key#10 --> btrfs_trans_num_writers --> btrfs_trans_num_extwriters
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
rlock(btrfs_trans_num_extwriters);
lock(btrfs_trans_num_writers);
lock(btrfs_trans_num_extwriters);
lock(&sb->s_type->i_mutex_key#10);
*** DEADLOCK ***
locks held by syz-executor324/6058: 3, last CPU#0:
#0: ffff8880139a2650 (sb_internal#2){.+.+}-{0:0}, at: btrfs_init_new_device+0x7f3/0x1cf0 fs/btrfs/volumes.c:3022
#1: ffff888027eb2680 (btrfs_trans_num_writers){.+.+}-{0:0}, at: join_transaction+0x6b2/0xd40 fs/btrfs/transaction.c:331
#2: ffff888027eb26a8 (btrfs_trans_num_extwriters){.+.+}-{0:0}, at: join_transaction+0x6b2/0xd40 fs/btrfs/transaction.c:331
stack backtrace:
CPU: 0 UID: 0 PID: 6058 Comm: syz-executor324 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/15/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087
check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219
check_prev_add kernel/locking/lockdep.c:3209 [inline]
check_prevs_add kernel/locking/lockdep.c:3328 [inline]
validate_chain kernel/locking/lockdep.c:3952 [inline]
__lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
down_write+0x91/0x200 kernel/locking/rwsem.c:1631
inode_lock include/linux/fs.h:1024 [inline]
set_blocksize+0x1e6/0x440 block/bdev.c:202
btrfs_init_new_device+0xa4e/0x1cf0 fs/btrfs/volumes.c:3046
btrfs_ioctl_add_dev+0x1ad/0x640 fs/btrfs/ioctl.c:2571
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f8612ea2ebb
Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00
RSP: 002b:00007ffe693cf9a0 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f8612ea2ebb
RDX: 00007ffe693d2bf0 RSI: 000000005000940a RDI: 0000000000000003
RBP: 00007ffe693d2bf0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffe693cfb20
R13: 0000000000000000 R14: 00007f8612e71000 R15: 00007ffe693cff70
</TASK>
---
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next reply other threads:[~2026-10-24 13:33 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-24 13:33 syzbot [this message]
-- strict thread matches above, loose matches on Subject: below --
2026-10-28 12:14 [PATCH] btrfs: set the block size before starting a transaction Qing Zhang
2026-10-28 13:01 ` [syzbot] [btrfs?] possible deadlock in set_blocksize syzbot
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