syzbot


possible deadlock in ext4_writepages

Status: upstream: reported syz repro on 2025/09/12 16:06
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+8c223a3aa6865f107658@syzkaller.appspotmail.com
First crash: 15h54m, last: 1h48m
Bug presence (1)
Date Name Commit Repro Result
2025/09/13 upstream (ToT) 22f20375f5b7 syz [report] possible deadlock in ext4_writepages
Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 possible deadlock in ext4_writepages 4 syz 11 2h12m 2d09h 0/3 upstream: reported syz repro on 2025/09/10 22:18
upstream possible deadlock in ext4_writepages ext4 4 1 1127d 1123d 0/29 auto-obsoleted due to no activity on 2022/12/11 07:00
upstream possible deadlock in ext4_writepages (2) ext4 4 C unreliable 50 23m 328d 0/29 upstream: reported C repro on 2024/10/19 20:27
linux-5.15 possible deadlock in ext4_writepages 4 2 863d 864d 0/3 auto-obsoleted due to no activity on 2023/08/23 09:09
linux-5.15 possible deadlock in ext4_writepages (2) 4 syz 2 2d11h 2d12h 0/3 upstream: reported syz repro on 2025/09/10 19:34

Sample crash report:
syz.0.17[5951]: memfd_create() called without MFD_EXEC or MFD_NOEXEC_SEAL set
loop0: detected capacity change from 0 to 512
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17/5951 is trying to acquire lock:
ffff88807bba4bd8 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages_down_read fs/ext4/ext4.h:1767 [inline]
ffff88807bba4bd8 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages+0x170/0x2f0 fs/ext4/inode.c:2806

but task is already holding lock:
ffff8880620680c8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_trylock_xattr fs/ext4/xattr.h:162 [inline]
ffff8880620680c8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_try_to_expand_extra_isize fs/ext4/inode.c:5993 [inline]
ffff8880620680c8 (&ei->xattr_sem){++++}-{3:3}, at: __ext4_mark_inode_dirty+0x3dc/0x6e0 fs/ext4/inode.c:6074

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&ei->xattr_sem){++++}-{3:3}:
       down_read+0x46/0x2e0 kernel/locking/rwsem.c:1520
       ext4_setattr+0x86b/0x1c90 fs/ext4/inode.c:5476
       notify_change+0xb0d/0xe10 fs/attr.c:499
       chown_common+0x3f9/0x5a0 fs/open.c:783
       do_fchownat+0x168/0x270 fs/open.c:814
       __do_sys_chown fs/open.c:834 [inline]
       __se_sys_chown fs/open.c:832 [inline]
       __x64_sys_chown+0x82/0x90 fs/open.c:832
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #1 (jbd2_handle){++++}-{0:0}:
       start_this_handle+0x1e9d/0x20c0 fs/jbd2/transaction.c:448
       jbd2__journal_start+0x2bb/0x5b0 fs/jbd2/transaction.c:505
       __ext4_journal_start_sb+0x203/0x570 fs/ext4/ext4_jbd2.c:112
       __ext4_journal_start fs/ext4/ext4_jbd2.h:326 [inline]
       ext4_do_writepages+0xf92/0x38d0 fs/ext4/inode.c:2701
       ext4_writepages+0x1a8/0x2f0 fs/ext4/inode.c:2807
       do_writepages+0x3a2/0x600 mm/page-writeback.c:2575
       __writeback_single_inode+0x153/0xee0 fs/fs-writeback.c:1625
       writeback_sb_inodes+0x77c/0xef0 fs/fs-writeback.c:1916
       __writeback_inodes_wb+0x111/0x240 fs/fs-writeback.c:1987
       wb_writeback+0x464/0xba0 fs/fs-writeback.c:2097
       wb_check_background_flush fs/fs-writeback.c:2167 [inline]
       wb_do_writeback fs/fs-writeback.c:2255 [inline]
       wb_workfn+0xb32/0xe20 fs/fs-writeback.c:2282
       process_one_work kernel/workqueue.c:2634 [inline]
       process_scheduled_works+0xa45/0x15b0 kernel/workqueue.c:2711
       worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
       kthread+0x2fa/0x390 kernel/kthread.c:388
       ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
       ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

-> #0 (&sbi->s_writepages_rwsem){++++}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3134 [inline]
       check_prevs_add kernel/locking/lockdep.c:3253 [inline]
       validate_chain kernel/locking/lockdep.c:3869 [inline]
       __lock_acquire+0x2ddb/0x7c80 kernel/locking/lockdep.c:5137
       lock_acquire+0x197/0x410 kernel/locking/lockdep.c:5754
       percpu_down_read+0x44/0x1a0 include/linux/percpu-rwsem.h:51
       ext4_writepages_down_read fs/ext4/ext4.h:1767 [inline]
       ext4_writepages+0x170/0x2f0 fs/ext4/inode.c:2806
       do_writepages+0x3a2/0x600 mm/page-writeback.c:2575
       __writeback_single_inode+0x153/0xee0 fs/fs-writeback.c:1625
       writeback_single_inode+0x211/0x720 fs/fs-writeback.c:1746
       write_inode_now+0x161/0x1e0 fs/fs-writeback.c:2792
       iput_final fs/inode.c:1807 [inline]
       iput+0x5b2/0x920 fs/inode.c:1846
       ext4_xattr_block_set+0x273a/0x32a0 fs/ext4/xattr.c:2206
       ext4_xattr_move_to_block fs/ext4/xattr.c:2674 [inline]
       ext4_xattr_make_inode_space fs/ext4/xattr.c:2749 [inline]
       ext4_expand_extra_isize_ea+0x10ea/0x19e0 fs/ext4/xattr.c:2841
       __ext4_expand_extra_isize+0x306/0x400 fs/ext4/inode.c:5953
       ext4_try_to_expand_extra_isize fs/ext4/inode.c:5996 [inline]
       __ext4_mark_inode_dirty+0x45d/0x6e0 fs/ext4/inode.c:6074
       ext4_evict_inode+0x7ed/0xea0 fs/ext4/inode.c:252
       evict+0x486/0x870 fs/inode.c:705
       ext4_orphan_cleanup+0xbd4/0x1400 fs/ext4/orphan.c:474
       __ext4_fill_super fs/ext4/super.c:5608 [inline]
       ext4_fill_super+0x5de7/0x66c0 fs/ext4/super.c:5731
       get_tree_bdev+0x3e4/0x510 fs/super.c:1591
       vfs_get_tree+0x8c/0x280 fs/super.c:1764
       do_new_mount+0x24b/0xa40 fs/namespace.c:3377
       do_mount fs/namespace.c:3717 [inline]
       __do_sys_mount fs/namespace.c:3926 [inline]
       __se_sys_mount+0x2da/0x3c0 fs/namespace.c:3903
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

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.0.17/5951:
 #0: ffff88807bba20e0 (&type->s_umount_key#31){++++}-{3:3}, at: __super_lock fs/super.c:56 [inline]
 #0: ffff88807bba20e0 (&type->s_umount_key#31){++++}-{3:3}, at: __super_lock_excl fs/super.c:71 [inline]
 #0: ffff88807bba20e0 (&type->s_umount_key#31){++++}-{3:3}, at: get_tree_bdev+0x344/0x510 fs/super.c:1589
 #1: ffff88807bba2608 (sb_internal){.+.+}-{0:0}, at: __sb_start_write include/linux/fs.h:1633 [inline]
 #1: ffff88807bba2608 (sb_internal){.+.+}-{0:0}, at: sb_start_intwrite include/linux/fs.h:1755 [inline]
 #1: ffff88807bba2608 (sb_internal){.+.+}-{0:0}, at: ext4_evict_inode+0x2b9/0xea0 fs/ext4/inode.c:213
 #2: ffff8880620680c8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_trylock_xattr fs/ext4/xattr.h:162 [inline]
 #2: ffff8880620680c8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_try_to_expand_extra_isize fs/ext4/inode.c:5993 [inline]
 #2: ffff8880620680c8 (&ei->xattr_sem){++++}-{3:3}, at: __ext4_mark_inode_dirty+0x3dc/0x6e0 fs/ext4/inode.c:6074

stack backtrace:
CPU: 1 PID: 5951 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x16c/0x230 lib/dump_stack.c:106
 check_noncircular+0x2bd/0x3c0 kernel/locking/lockdep.c:2187
 check_prev_add kernel/locking/lockdep.c:3134 [inline]
 check_prevs_add kernel/locking/lockdep.c:3253 [inline]
 validate_chain kernel/locking/lockdep.c:3869 [inline]
 __lock_acquire+0x2ddb/0x7c80 kernel/locking/lockdep.c:5137
 lock_acquire+0x197/0x410 kernel/locking/lockdep.c:5754
 percpu_down_read+0x44/0x1a0 include/linux/percpu-rwsem.h:51
 ext4_writepages_down_read fs/ext4/ext4.h:1767 [inline]
 ext4_writepages+0x170/0x2f0 fs/ext4/inode.c:2806
 do_writepages+0x3a2/0x600 mm/page-writeback.c:2575
 __writeback_single_inode+0x153/0xee0 fs/fs-writeback.c:1625
 writeback_single_inode+0x211/0x720 fs/fs-writeback.c:1746
 write_inode_now+0x161/0x1e0 fs/fs-writeback.c:2792
 iput_final fs/inode.c:1807 [inline]
 iput+0x5b2/0x920 fs/inode.c:1846
 ext4_xattr_block_set+0x273a/0x32a0 fs/ext4/xattr.c:2206
 ext4_xattr_move_to_block fs/ext4/xattr.c:2674 [inline]
 ext4_xattr_make_inode_space fs/ext4/xattr.c:2749 [inline]
 ext4_expand_extra_isize_ea+0x10ea/0x19e0 fs/ext4/xattr.c:2841
 __ext4_expand_extra_isize+0x306/0x400 fs/ext4/inode.c:5953
 ext4_try_to_expand_extra_isize fs/ext4/inode.c:5996 [inline]
 __ext4_mark_inode_dirty+0x45d/0x6e0 fs/ext4/inode.c:6074
 ext4_evict_inode+0x7ed/0xea0 fs/ext4/inode.c:252
 evict+0x486/0x870 fs/inode.c:705
 ext4_orphan_cleanup+0xbd4/0x1400 fs/ext4/orphan.c:474
 __ext4_fill_super fs/ext4/super.c:5608 [inline]
 ext4_fill_super+0x5de7/0x66c0 fs/ext4/super.c:5731
 get_tree_bdev+0x3e4/0x510 fs/super.c:1591
 vfs_get_tree+0x8c/0x280 fs/super.c:1764
 do_new_mount+0x24b/0xa40 fs/namespace.c:3377
 do_mount fs/namespace.c:3717 [inline]
 __do_sys_mount fs/namespace.c:3926 [inline]
 __se_sys_mount+0x2da/0x3c0 fs/namespace.c:3903
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f3af759034a
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:00007ffd2e0bbb48 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007ffd2e0bbbd0 RCX: 00007f3af759034a
RDX: 0000200000000180 RSI: 00002000000001c0 RDI: 00007ffd2e0bbb90
RBP: 0000200000000180 R08: 00007ffd2e0bbbd0 R09: 0000000000800700
R10: 0000000000800700 R11: 0000000000000246 R12: 00002000000001c0
R13: 00007ffd2e0bbb90 R14: 0000000000000473 R15: 0000200000000680
 </TASK>
------------[ cut here ]------------
EA inode 11 i_nlink=2
WARNING: CPU: 1 PID: 5951 at fs/ext4/xattr.c:1070 ext4_xattr_inode_update_ref+0x521/0x580 fs/ext4/xattr.c:1068
Modules linked in:
CPU: 1 PID: 5951 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:ext4_xattr_inode_update_ref+0x521/0x580 fs/ext4/xattr.c:1068
Code: 24 50 4c 89 f8 48 c1 e8 03 42 80 3c 28 00 74 08 4c 89 ff e8 31 43 9a ff 49 8b 37 48 c7 c7 00 d1 be 8a 44 89 f2 e8 cf 73 0d ff <0f> 0b 4c 8b 64 24 18 48 8b 5c 24 10 4c 8d 7c 24 60 e9 1f fe ff ff
RSP: 0018:ffffc90003417220 EFLAGS: 00010246
RAX: b80b0b09e414da00 RBX: 0000000000000001 RCX: ffff88802b558000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
RBP: ffffc90003417318 R08: ffffc90003416e27 R09: 1ffff92000682dc4
R10: dffffc0000000000 R11: fffff52000682dc5 R12: ffff88806206a0b0
R13: dffffc0000000000 R14: 0000000000000002 R15: ffff88806206a100
FS:  000055556cc81500(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f07c7bb3000 CR3: 000000002d872000 CR4: 00000000003506e0
Call Trace:
 <TASK>
 ext4_xattr_inode_dec_ref fs/ext4/xattr.c:1093 [inline]
 ext4_xattr_set_entry+0xcda/0x1e90 fs/ext4/xattr.c:1731
 ext4_xattr_ibody_set+0x254/0x6a0 fs/ext4/xattr.c:2278
 ext4_xattr_move_to_block fs/ext4/xattr.c:2681 [inline]
 ext4_xattr_make_inode_space fs/ext4/xattr.c:2749 [inline]
 ext4_expand_extra_isize_ea+0x113a/0x19e0 fs/ext4/xattr.c:2841
 __ext4_expand_extra_isize+0x306/0x400 fs/ext4/inode.c:5953
 ext4_try_to_expand_extra_isize fs/ext4/inode.c:5996 [inline]
 __ext4_mark_inode_dirty+0x45d/0x6e0 fs/ext4/inode.c:6074
 ext4_evict_inode+0x7ed/0xea0 fs/ext4/inode.c:252
 evict+0x486/0x870 fs/inode.c:705
 ext4_orphan_cleanup+0xbd4/0x1400 fs/ext4/orphan.c:474
 __ext4_fill_super fs/ext4/super.c:5608 [inline]
 ext4_fill_super+0x5de7/0x66c0 fs/ext4/super.c:5731
 get_tree_bdev+0x3e4/0x510 fs/super.c:1591
 vfs_get_tree+0x8c/0x280 fs/super.c:1764
 do_new_mount+0x24b/0xa40 fs/namespace.c:3377
 do_mount fs/namespace.c:3717 [inline]
 __do_sys_mount fs/namespace.c:3926 [inline]
 __se_sys_mount+0x2da/0x3c0 fs/namespace.c:3903
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f3af759034a
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:00007ffd2e0bbb48 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007ffd2e0bbbd0 RCX: 00007f3af759034a
RDX: 0000200000000180 RSI: 00002000000001c0 RDI: 00007ffd2e0bbb90
RBP: 0000200000000180 R08: 00007ffd2e0bbbd0 R09: 0000000000800700
R10: 0000000000800700 R11: 0000000000000246 R12: 00002000000001c0
R13: 00007ffd2e0bbb90 R14: 0000000000000473 R15: 0000200000000680
 </TASK>

Crashes (10):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/09/13 06:12 linux-6.6.y 60a9e718726f e2beed91 .config console log report syz / log [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-6-6-kasan possible deadlock in ext4_writepages
2025/09/13 05:29 linux-6.6.y 60a9e718726f e2beed91 .config console log report syz / log [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-6-6-kasan possible deadlock in ext4_writepages
2025/09/13 05:02 linux-6.6.y 60a9e718726f e2beed91 .config console log report syz / log [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-6-6-kasan possible deadlock in ext4_writepages
2025/09/12 16:51 linux-6.6.y 60a9e718726f e2beed91 .config console log report syz / log [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-6-6-kasan possible deadlock in ext4_writepages
2025/09/12 16:30 linux-6.6.y 60a9e718726f e2beed91 .config console log report syz / log [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-6-6-kasan possible deadlock in ext4_writepages
2025/09/13 04:39 linux-6.6.y 60a9e718726f e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in ext4_writepages
2025/09/13 04:35 linux-6.6.y 60a9e718726f e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in ext4_writepages
2025/09/13 04:35 linux-6.6.y 60a9e718726f e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in ext4_writepages
2025/09/12 16:06 linux-6.6.y 60a9e718726f e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in ext4_writepages
2025/09/12 16:05 linux-6.6.y 60a9e718726f e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in ext4_writepages
* Struck through repros no longer work on HEAD.