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Message-ID: <6933d1f5.a70a0220.38f243.0016.GAE@google.com>
Date: Fri, 05 Dec 2025 22:49:25 -0800
From: syzbot <syzbot+756f498a88797cda9299@...kaller.appspotmail.com>
To: akpm@...ux-foundation.org, linux-ext4@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, syzkaller-bugs@...glegroups.com, willy@...radead.org
Subject: Re: [syzbot] [ext4?] possible deadlock in do_writepages (2)
syzbot has found a reproducer for the following issue on:
HEAD commit: d1d36025a617 Merge tag 'probes-v6.19' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17c5821a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=96b1065fc3079f82
dashboard link: https://syzkaller.appspot.com/bug?extid=756f498a88797cda9299
compiler: gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10133c1a580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16178992580000
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/01358f3e734d/disk-d1d36025.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8c72ac5de2c8/vmlinux-d1d36025.xz
kernel image: https://storage.googleapis.com/syzbot-assets/44b0ffcb520c/bzImage-d1d36025.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/8c26f8a66fe2/mount_0.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=12bc02c2580000)
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+756f498a88797cda9299@...kaller.appspotmail.com
loop0: detected capacity change from 0 to 512
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17/6041 is trying to acquire lock:
ffff88803394eb98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: do_writepages+0x27a/0x600 mm/page-writeback.c:2598
but task is already holding lock:
ffff888059c16aa8 (&ei->xattr_sem){++++}-{4:4}, at: ext4_write_trylock_xattr fs/ext4/xattr.h:164 [inline]
ffff888059c16aa8 (&ei->xattr_sem){++++}-{4:4}, at: ext4_try_to_expand_extra_isize fs/ext4/inode.c:6389 [inline]
ffff888059c16aa8 (&ei->xattr_sem){++++}-{4:4}, at: __ext4_mark_inode_dirty+0x4ba/0x840 fs/ext4/inode.c:6470
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (&ei->xattr_sem){++++}-{4:4}:
down_read+0x9b/0x460 kernel/locking/rwsem.c:1537
ext4_setattr+0x869/0x28d0 fs/ext4/inode.c:5865
notify_change+0x6d2/0x1290 fs/attr.c:546
chown_common+0x549/0x680 fs/open.c:788
do_fchownat+0x1a7/0x200 fs/open.c:819
__do_sys_chown fs/open.c:839 [inline]
__se_sys_chown fs/open.c:837 [inline]
__x64_sys_chown+0x7b/0xc0 fs/open.c:837
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #1 (jbd2_handle){++++}-{0:0}:
wait_transaction_locked+0x191/0x230 fs/jbd2/transaction.c:151
add_transaction_credits+0x110/0xe60 fs/jbd2/transaction.c:222
start_this_handle+0x3e7/0x1410 fs/jbd2/transaction.c:403
jbd2__journal_start+0x394/0x6a0 fs/jbd2/transaction.c:501
__ext4_journal_start_sb+0x195/0x640 fs/ext4/ext4_jbd2.c:114
__ext4_journal_start fs/ext4/ext4_jbd2.h:242 [inline]
ext4_do_writepages+0xc23/0x3c70 fs/ext4/inode.c:2914
ext4_writepages+0x37a/0x7d0 fs/ext4/inode.c:3026
do_writepages+0x27a/0x600 mm/page-writeback.c:2598
__writeback_single_inode+0x168/0x14a0 fs/fs-writeback.c:1737
writeback_sb_inodes+0x795/0x1de0 fs/fs-writeback.c:2030
__writeback_inodes_wb+0xf8/0x2d0 fs/fs-writeback.c:2107
wb_writeback+0x799/0xae0 fs/fs-writeback.c:2218
wb_check_old_data_flush fs/fs-writeback.c:2322 [inline]
wb_do_writeback fs/fs-writeback.c:2375 [inline]
wb_workfn+0x8a0/0xbb0 fs/fs-writeback.c:2403
process_one_work+0x9ba/0x1b20 kernel/workqueue.c:3257
process_scheduled_works kernel/workqueue.c:3340 [inline]
worker_thread+0x6c8/0xf10 kernel/workqueue.c:3421
kthread+0x3c5/0x780 kernel/kthread.c:463
ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
-> #0 (&sbi->s_writepages_rwsem){++++}-{0:0}:
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x1542/0x22f0 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x179/0x330 kernel/locking/lockdep.c:5825
percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
ext4_writepages_down_read fs/ext4/ext4.h:1820 [inline]
ext4_writepages+0x224/0x7d0 fs/ext4/inode.c:3025
do_writepages+0x27a/0x600 mm/page-writeback.c:2598
__writeback_single_inode+0x168/0x14a0 fs/fs-writeback.c:1737
writeback_single_inode+0x5ea/0x11f0 fs/fs-writeback.c:1858
write_inode_now+0x170/0x1e0 fs/fs-writeback.c:2924
iput_final fs/inode.c:1941 [inline]
iput.part.0+0x815/0x1190 fs/inode.c:2003
iput+0x35/0x40 fs/inode.c:1966
ext4_xattr_block_set+0x67c/0x3640 fs/ext4/xattr.c:2203
ext4_xattr_move_to_block fs/ext4/xattr.c:2668 [inline]
ext4_xattr_make_inode_space fs/ext4/xattr.c:2743 [inline]
ext4_expand_extra_isize_ea+0x1442/0x1ab0 fs/ext4/xattr.c:2831
__ext4_expand_extra_isize+0x346/0x480 fs/ext4/inode.c:6349
ext4_try_to_expand_extra_isize fs/ext4/inode.c:6392 [inline]
__ext4_mark_inode_dirty+0x544/0x840 fs/ext4/inode.c:6470
ext4_evict_inode+0x713/0x1730 fs/ext4/inode.c:253
evict+0x3c2/0xad0 fs/inode.c:837
iput_final fs/inode.c:1951 [inline]
iput.part.0+0x621/0x1190 fs/inode.c:2003
iput+0x35/0x40 fs/inode.c:1966
ext4_orphan_cleanup+0x731/0x11e0 fs/ext4/orphan.c:472
__ext4_fill_super fs/ext4/super.c:5658 [inline]
ext4_fill_super+0x7ec1/0xb570 fs/ext4/super.c:5777
get_tree_bdev_flags+0x38c/0x620 fs/super.c:1699
vfs_get_tree+0x8e/0x330 fs/super.c:1759
fc_mount fs/namespace.c:1199 [inline]
do_new_mount_fc fs/namespace.c:3636 [inline]
do_new_mount fs/namespace.c:3712 [inline]
path_mount+0x7bf/0x23a0 fs/namespace.c:4022
do_mount fs/namespace.c:4035 [inline]
__do_sys_mount fs/namespace.c:4224 [inline]
__se_sys_mount fs/namespace.c:4201 [inline]
__x64_sys_mount+0x293/0x310 fs/namespace.c:4201
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
other info that might help us debug this:
Chain exists of:
&sbi->s_writepages_rwsem --> jbd2_handle --> &ei->xattr_sem
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&ei->xattr_sem);
lock(jbd2_handle);
lock(&ei->xattr_sem);
rlock(&sbi->s_writepages_rwsem);
*** DEADLOCK ***
3 locks held by syz.0.17/6041:
#0: ffff88803394c0e0 (&type->s_umount_key#27/1){+.+.}-{4:4}, at: alloc_super+0x244/0xd00 fs/super.c:344
#1: ffff88803394c610 (sb_internal){.+.+}-{0:0}, at: evict+0x3c2/0xad0 fs/inode.c:837
#2: ffff888059c16aa8 (&ei->xattr_sem){++++}-{4:4}, at: ext4_write_trylock_xattr fs/ext4/xattr.h:164 [inline]
#2: ffff888059c16aa8 (&ei->xattr_sem){++++}-{4:4}, at: ext4_try_to_expand_extra_isize fs/ext4/inode.c:6389 [inline]
#2: ffff888059c16aa8 (&ei->xattr_sem){++++}-{4:4}, at: __ext4_mark_inode_dirty+0x4ba/0x840 fs/ext4/inode.c:6470
stack backtrace:
CPU: 1 UID: 0 PID: 6041 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
print_circular_bug+0x2db/0x410 kernel/locking/lockdep.c:2043
check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2175
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x1542/0x22f0 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x179/0x330 kernel/locking/lockdep.c:5825
percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
ext4_writepages_down_read fs/ext4/ext4.h:1820 [inline]
ext4_writepages+0x224/0x7d0 fs/ext4/inode.c:3025
do_writepages+0x27a/0x600 mm/page-writeback.c:2598
__writeback_single_inode+0x168/0x14a0 fs/fs-writeback.c:1737
writeback_single_inode+0x5ea/0x11f0 fs/fs-writeback.c:1858
write_inode_now+0x170/0x1e0 fs/fs-writeback.c:2924
iput_final fs/inode.c:1941 [inline]
iput.part.0+0x815/0x1190 fs/inode.c:2003
iput+0x35/0x40 fs/inode.c:1966
ext4_xattr_block_set+0x67c/0x3640 fs/ext4/xattr.c:2203
ext4_xattr_move_to_block fs/ext4/xattr.c:2668 [inline]
ext4_xattr_make_inode_space fs/ext4/xattr.c:2743 [inline]
ext4_expand_extra_isize_ea+0x1442/0x1ab0 fs/ext4/xattr.c:2831
__ext4_expand_extra_isize+0x346/0x480 fs/ext4/inode.c:6349
ext4_try_to_expand_extra_isize fs/ext4/inode.c:6392 [inline]
__ext4_mark_inode_dirty+0x544/0x840 fs/ext4/inode.c:6470
ext4_evict_inode+0x713/0x1730 fs/ext4/inode.c:253
evict+0x3c2/0xad0 fs/inode.c:837
iput_final fs/inode.c:1951 [inline]
iput.part.0+0x621/0x1190 fs/inode.c:2003
iput+0x35/0x40 fs/inode.c:1966
ext4_orphan_cleanup+0x731/0x11e0 fs/ext4/orphan.c:472
__ext4_fill_super fs/ext4/super.c:5658 [inline]
ext4_fill_super+0x7ec1/0xb570 fs/ext4/super.c:5777
get_tree_bdev_flags+0x38c/0x620 fs/super.c:1699
vfs_get_tree+0x8e/0x330 fs/super.c:1759
fc_mount fs/namespace.c:1199 [inline]
do_new_mount_fc fs/namespace.c:3636 [inline]
do_new_mount fs/namespace.c:3712 [inline]
path_mount+0x7bf/0x23a0 fs/namespace.c:4022
do_mount fs/namespace.c:4035 [inline]
__do_sys_mount fs/namespace.c:4224 [inline]
__se_sys_mount fs/namespace.c:4201 [inline]
__x64_sys_mount+0x293/0x310 fs/namespace.c:4201
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f24b8790eea
Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 de 1a 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe9c113938 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007ffe9c1139c0 RCX: 00007f24b8790eea
RDX: 0000200000000180 RSI: 00002000000001c0 RDI: 00007ffe9c113980
RBP: 0000200000000180 R08: 00007ffe9c1139c0 R09: 0000000000800700
R10: 0000000000800700 R11: 0000000000000246 R12: 00002000000001c0
R13: 00007ffe9c113980 R14: 000000000000046f R15: 000000000000002c
</TASK>
------------[ cut here ]------------
EA inode 11 i_nlink=2
WARNING: fs/ext4/xattr.c:1056 at 0x0, CPU#0: syz.0.17/6041
Modules linked in:
CPU: 0 UID: 0 PID: 6041 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:ext4_xattr_inode_update_ref+0x4be/0x5b0 fs/ext4/xattr.c:1056
Code: 40 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 f1 00 00 00 48 8d 3d 09 d6 fb 0d 48 8b 73 40 44 89 e2 <67> 48 0f b9 3a e9 06 ff ff ff e8 23 c7 2c ff 48 8d 7b 40 48 b8 00
RSP: 0018:ffffc900033c7178 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffff888059d59f78 RCX: ffffffff82915db4
RDX: 0000000000000002 RSI: 000000000000000b RDI: ffffffff908d34b0
RBP: ffffc900033c7240 R08: 0000000000000005 R09: 0000000000000001
R10: 0000000000000002 R11: 0000000000000001 R12: 0000000000000002
R13: ffffffffffffffff R14: 1ffff92000678e32 R15: ffff888059d5a168
FS: 00005555694d6500(0000) GS:ffff88812495e000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005641e7f0f078 CR3: 00000000744a9000 CR4: 0000000000350ef0
Call Trace:
<TASK>
ext4_xattr_inode_dec_ref fs/ext4/xattr.c:1081 [inline]
ext4_xattr_set_entry+0x158f/0x1f00 fs/ext4/xattr.c:1723
ext4_xattr_ibody_set+0x3d6/0x5d0 fs/ext4/xattr.c:2272
ext4_xattr_move_to_block fs/ext4/xattr.c:2675 [inline]
ext4_xattr_make_inode_space fs/ext4/xattr.c:2743 [inline]
ext4_expand_extra_isize_ea+0x148c/0x1ab0 fs/ext4/xattr.c:2831
__ext4_expand_extra_isize+0x346/0x480 fs/ext4/inode.c:6349
ext4_try_to_expand_extra_isize fs/ext4/inode.c:6392 [inline]
__ext4_mark_inode_dirty+0x544/0x840 fs/ext4/inode.c:6470
ext4_evict_inode+0x713/0x1730 fs/ext4/inode.c:253
evict+0x3c2/0xad0 fs/inode.c:837
iput_final fs/inode.c:1951 [inline]
iput.part.0+0x621/0x1190 fs/inode.c:2003
iput+0x35/0x40 fs/inode.c:1966
ext4_orphan_cleanup+0x731/0x11e0 fs/ext4/orphan.c:472
__ext4_fill_super fs/ext4/super.c:5658 [inline]
ext4_fill_super+0x7ec1/0xb570 fs/ext4/super.c:5777
get_tree_bdev_flags+0x38c/0x620 fs/super.c:1699
vfs_get_tree+0x8e/0x330 fs/super.c:1759
fc_mount fs/namespace.c:1199 [inline]
do_new_mount_fc fs/namespace.c:3636 [inline]
do_new_mount fs/namespace.c:3712 [inline]
path_mount+0x7bf/0x23a0 fs/namespace.c:4022
do_mount fs/namespace.c:4035 [inline]
__do_sys_mount fs/namespace.c:4224 [inline]
__se_sys_mount fs/namespace.c:4201 [inline]
__x64_sys_mount+0x293/0x310 fs/namespace.c:4201
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f24b8790eea
Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 de 1a 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe9c113938 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007ffe9c1139c0 RCX: 00007f24b8790eea
RDX: 0000200000000180 RSI: 00002000000001c0 RDI: 00007ffe9c113980
RBP: 0000200000000180 R08: 00007ffe9c1139c0 R09: 0000000000800700
R10: 0000000000800700 R11: 0000000000000246 R12: 00002000000001c0
R13: 00007ffe9c113980 R14: 000000000000046f R15: 000000000000002c
</TASK>
----------------
Code disassembly (best guess):
0: 40 rex
1: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
8: fc ff df
b: 48 89 fa mov %rdi,%rdx
e: 48 c1 ea 03 shr $0x3,%rdx
12: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1)
16: 0f 85 f1 00 00 00 jne 0x10d
1c: 48 8d 3d 09 d6 fb 0d lea 0xdfbd609(%rip),%rdi # 0xdfbd62c
23: 48 8b 73 40 mov 0x40(%rbx),%rsi
27: 44 89 e2 mov %r12d,%edx
* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2f: e9 06 ff ff ff jmp 0xffffff3a
34: e8 23 c7 2c ff call 0xff2cc75c
39: 48 8d 7b 40 lea 0x40(%rbx),%rdi
3d: 48 rex.W
3e: b8 .byte 0xb8
---
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.
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