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possible deadlock in ext4_writepages

Status: upstream: reported syz repro on 2025/09/10 22:18
Reported-by: syzbot+0bacd77c29cb89886c3a@syzkaller.appspotmail.com
First crash: 2d07h, last: 34m
▶ ▼ Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in ext4_writepages ext4 4 1 1126d 1122d 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 49 1h56m 328d 0/29 upstream: reported C repro on 2024/10/19 20:27
linux-6.6 possible deadlock in ext4_writepages 4 syz 9 17m 13h40m 0/2 upstream: reported syz repro on 2025/09/12 16:06
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 2d09h 2d10h 0/3 upstream: reported syz repro on 2025/09/10 19:34

Sample crash report:
loop0: detected capacity change from 0 to 512
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17/4491 is trying to acquire lock:
ffff0000d3538b98 (&sbi->s_writepages_rwsem){.+.+}-{0:0}, at: ext4_writepages+0x188/0x284c fs/ext4/inode.c:2715

but task is already holding lock:
ffff0000e9dadb10 (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_trylock_xattr fs/ext4/xattr.h:162 [inline]
ffff0000e9dadb10 (&ei->xattr_sem){++++}-{3:3}, at: ext4_try_to_expand_extra_isize fs/ext4/inode.c:6006 [inline]
ffff0000e9dadb10 (&ei->xattr_sem){++++}-{3:3}, at: __ext4_mark_inode_dirty+0x37c/0x790 fs/ext4/inode.c:6087

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&ei->xattr_sem){++++}-{3:3}:
       down_read+0x64/0x304 kernel/locking/rwsem.c:1520
       ext4_setattr+0x7c4/0x150c fs/ext4/inode.c:5501
       notify_change+0xb0c/0xdcc fs/attr.c:499
       chown_common+0x414/0x574 fs/open.c:736
       do_fchownat+0x158/0x268 fs/open.c:767
       __do_sys_fchownat fs/open.c:782 [inline]
       __se_sys_fchownat fs/open.c:779 [inline]
       __arm64_sys_fchownat+0xb8/0xd4 fs/open.c:779
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x138 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #1 (jbd2_handle){++++}-{0:0}:
       start_this_handle+0xfe0/0x122c fs/jbd2/transaction.c:463
       jbd2__journal_start+0x288/0x51c fs/jbd2/transaction.c:520
       __ext4_journal_start_sb+0x2fc/0x674 fs/ext4/ext4_jbd2.c:105
       __ext4_journal_start fs/ext4/ext4_jbd2.h:326 [inline]
       ext4_writepages+0xa28/0x284c fs/ext4/inode.c:2838
       do_writepages+0x2c0/0x4fc mm/page-writeback.c:2491
       __writeback_single_inode+0x164/0x157c fs/fs-writeback.c:1612
       writeback_sb_inodes+0x824/0x1404 fs/fs-writeback.c:1903
       __writeback_inodes_wb+0x110/0x394 fs/fs-writeback.c:1974
       wb_writeback+0x414/0xfb0 fs/fs-writeback.c:2079
       wb_check_background_flush fs/fs-writeback.c:2145 [inline]
       wb_do_writeback fs/fs-writeback.c:2233 [inline]
       wb_workfn+0xac0/0xd98 fs/fs-writeback.c:2260
       process_one_work+0x7f4/0x13a8 kernel/workqueue.c:2292
       worker_thread+0x8c8/0xfbc kernel/workqueue.c:2439
       kthread+0x250/0x2d8 kernel/kthread.c:376
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:850

-> #0 (&sbi->s_writepages_rwsem){.+.+}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3090 [inline]
       check_prevs_add kernel/locking/lockdep.c:3209 [inline]
       validate_chain kernel/locking/lockdep.c:3825 [inline]
       __lock_acquire+0x293c/0x6544 kernel/locking/lockdep.c:5049
       lock_acquire+0x20c/0x644 kernel/locking/lockdep.c:5662
       percpu_down_read+0x70/0x2a8 include/linux/percpu-rwsem.h:51
       ext4_writepages+0x188/0x284c fs/ext4/inode.c:2715
       do_writepages+0x2c0/0x4fc mm/page-writeback.c:2491
       __writeback_single_inode+0x164/0x157c fs/fs-writeback.c:1612
       writeback_single_inode+0x1c0/0x720 fs/fs-writeback.c:1733
       write_inode_now+0x144/0x1b0 fs/fs-writeback.c:2770
       iput_final fs/inode.c:1821 [inline]
       iput+0x5cc/0x7f4 fs/inode.c:1860
       ext4_xattr_block_set+0x17a4/0x2810 fs/ext4/xattr.c:2157
       ext4_xattr_move_to_block fs/ext4/xattr.c:2625 [inline]
       ext4_xattr_make_inode_space fs/ext4/xattr.c:2700 [inline]
       ext4_expand_extra_isize_ea+0xcb8/0x15cc fs/ext4/xattr.c:2792
       __ext4_expand_extra_isize+0x298/0x358 fs/ext4/inode.c:5966
       ext4_try_to_expand_extra_isize fs/ext4/inode.c:6009 [inline]
       __ext4_mark_inode_dirty+0x3e4/0x790 fs/ext4/inode.c:6087
       ext4_evict_inode+0xb58/0x1270 fs/ext4/inode.c:279
       evict+0x3c8/0x810 fs/inode.c:705
       iput_final fs/inode.c:1834 [inline]
       iput+0x764/0x7f4 fs/inode.c:1860
       ext4_process_orphan+0x240/0x2b4 fs/ext4/orphan.c:360
       ext4_orphan_cleanup+0x908/0x104c fs/ext4/orphan.c:474
       __ext4_fill_super fs/ext4/super.c:5537 [inline]
       ext4_fill_super+0x6920/0x6e34 fs/ext4/super.c:5668
       get_tree_bdev+0x358/0x544 fs/super.c:1366
       ext4_get_tree+0x28/0x38 fs/ext4/super.c:5698
       vfs_get_tree+0x90/0x274 fs/super.c:1573
       do_new_mount+0x228/0x810 fs/namespace.c:3069
       path_mount+0x5b4/0xe78 fs/namespace.c:3399
       do_mount fs/namespace.c:3412 [inline]
       __do_sys_mount fs/namespace.c:3620 [inline]
       __se_sys_mount fs/namespace.c:3597 [inline]
       __arm64_sys_mount+0x49c/0x584 fs/namespace.c:3597
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x138 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

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);
  lock(&sbi->s_writepages_rwsem);

 *** DEADLOCK ***

3 locks held by syz.0.17/4491:
 #0: ffff0000d353a0e0 (&type->s_umount_key#26/1){+.+.}-{3:3}, at: alloc_super+0x1a4/0x804 fs/super.c:228
 #1: ffff0000d353a650 (sb_internal){.+.+}-{0:0}, at: __sb_start_write include/linux/fs.h:1891 [inline]
 #1: ffff0000d353a650 (sb_internal){.+.+}-{0:0}, at: sb_start_intwrite include/linux/fs.h:2013 [inline]
 #1: ffff0000d353a650 (sb_internal){.+.+}-{0:0}, at: ext4_evict_inode+0x3dc/0x1270 fs/ext4/inode.c:240
 #2: ffff0000e9dadb10 (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_trylock_xattr fs/ext4/xattr.h:162 [inline]
 #2: ffff0000e9dadb10 (&ei->xattr_sem){++++}-{3:3}, at: ext4_try_to_expand_extra_isize fs/ext4/inode.c:6006 [inline]
 #2: ffff0000e9dadb10 (&ei->xattr_sem){++++}-{3:3}, at: __ext4_mark_inode_dirty+0x37c/0x790 fs/ext4/inode.c:6087

stack backtrace:
CPU: 1 PID: 4491 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025
Call trace:
 dump_backtrace+0x1c8/0x1f4 arch/arm64/kernel/stacktrace.c:158
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
 __dump_stack+0x30/0x40 lib/dump_stack.c:88
 dump_stack_lvl+0xf8/0x160 lib/dump_stack.c:106
 dump_stack+0x1c/0x5c lib/dump_stack.c:113
 print_circular_bug+0x148/0x1b0 kernel/locking/lockdep.c:2048
 check_noncircular+0x240/0x2d4 kernel/locking/lockdep.c:2170
 check_prev_add kernel/locking/lockdep.c:3090 [inline]
 check_prevs_add kernel/locking/lockdep.c:3209 [inline]
 validate_chain kernel/locking/lockdep.c:3825 [inline]
 __lock_acquire+0x293c/0x6544 kernel/locking/lockdep.c:5049
 lock_acquire+0x20c/0x644 kernel/locking/lockdep.c:5662
 percpu_down_read+0x70/0x2a8 include/linux/percpu-rwsem.h:51
 ext4_writepages+0x188/0x284c fs/ext4/inode.c:2715
 do_writepages+0x2c0/0x4fc mm/page-writeback.c:2491
 __writeback_single_inode+0x164/0x157c fs/fs-writeback.c:1612
 writeback_single_inode+0x1c0/0x720 fs/fs-writeback.c:1733
 write_inode_now+0x144/0x1b0 fs/fs-writeback.c:2770
 iput_final fs/inode.c:1821 [inline]
 iput+0x5cc/0x7f4 fs/inode.c:1860
 ext4_xattr_block_set+0x17a4/0x2810 fs/ext4/xattr.c:2157
 ext4_xattr_move_to_block fs/ext4/xattr.c:2625 [inline]
 ext4_xattr_make_inode_space fs/ext4/xattr.c:2700 [inline]
 ext4_expand_extra_isize_ea+0xcb8/0x15cc fs/ext4/xattr.c:2792
 __ext4_expand_extra_isize+0x298/0x358 fs/ext4/inode.c:5966
 ext4_try_to_expand_extra_isize fs/ext4/inode.c:6009 [inline]
 __ext4_mark_inode_dirty+0x3e4/0x790 fs/ext4/inode.c:6087
 ext4_evict_inode+0xb58/0x1270 fs/ext4/inode.c:279
 evict+0x3c8/0x810 fs/inode.c:705
 iput_final fs/inode.c:1834 [inline]
 iput+0x764/0x7f4 fs/inode.c:1860
 ext4_process_orphan+0x240/0x2b4 fs/ext4/orphan.c:360
 ext4_orphan_cleanup+0x908/0x104c fs/ext4/orphan.c:474
 __ext4_fill_super fs/ext4/super.c:5537 [inline]
 ext4_fill_super+0x6920/0x6e34 fs/ext4/super.c:5668
 get_tree_bdev+0x358/0x544 fs/super.c:1366
 ext4_get_tree+0x28/0x38 fs/ext4/super.c:5698
 vfs_get_tree+0x90/0x274 fs/super.c:1573
 do_new_mount+0x228/0x810 fs/namespace.c:3069
 path_mount+0x5b4/0xe78 fs/namespace.c:3399
 do_mount fs/namespace.c:3412 [inline]
 __do_sys_mount fs/namespace.c:3620 [inline]
 __se_sys_mount fs/namespace.c:3597 [inline]
 __arm64_sys_mount+0x49c/0x584 fs/namespace.c:3597
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x138 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585
------------[ cut here ]------------
EA inode 11 i_nlink=2
WARNING: CPU: 0 PID: 4491 at fs/ext4/xattr.c:1021 ext4_xattr_inode_update_ref+0x468/0x4ac fs/ext4/xattr.c:-1
Modules linked in:
CPU: 0 PID: 4491 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025
pstate: 62400005 (nZCv daif +PAN -UAO +TCO -DIT -SSBS BTYPE=--)
pc : ext4_xattr_inode_update_ref+0x468/0x4ac fs/ext4/xattr.c:-1
lr : ext4_xattr_inode_update_ref+0x464/0x4ac fs/ext4/xattr.c:1019
sp : ffff800021556e80
x29: ffff800021556f00 x28: 0000000000000000 x27: dfff800000000000
x26: 1fffe0001d3a9e60 x25: ffff7000042aadd0 x24: 0000000000000000
x23: ffff800017a8b000 x22: ffff800021556e80 x21: 0000000000000002
x20: 0000000000000001 x19: ffff0000e9d4f108 x18: ffff800011abbcc0
x17: 0000000000000000 x16: ffff800008042c8c x15: 0000000000000000
x14: 00000000ffffffff x13: 0000000000000001 x12: 0000000000ff0100
x11: ff00800008191ca8 x10: 0000000000000000 x9 : 33938078b585b800
x8 : 33938078b585b800 x7 : 0000000000000001 x6 : 0000000000000001
x5 : ffff800021556918 x4 : ffff8000151a4820 x3 : ffff80000852e404
x2 : 0000000000000001 x1 : 0000000100000000 x0 : 0000000000000000
Call trace:
 ext4_xattr_inode_update_ref+0x468/0x4ac fs/ext4/xattr.c:-1
 ext4_xattr_inode_dec_ref fs/ext4/xattr.c:1044 [inline]
 ext4_xattr_set_entry+0x918/0x15ac fs/ext4/xattr.c:1682
 ext4_xattr_ibody_set+0x204/0x600 fs/ext4/xattr.c:2229
 ext4_xattr_move_to_block fs/ext4/xattr.c:2632 [inline]
 ext4_xattr_make_inode_space fs/ext4/xattr.c:2700 [inline]
 ext4_expand_extra_isize_ea+0xd00/0x15cc fs/ext4/xattr.c:2792
 __ext4_expand_extra_isize+0x298/0x358 fs/ext4/inode.c:5966
 ext4_try_to_expand_extra_isize fs/ext4/inode.c:6009 [inline]
 __ext4_mark_inode_dirty+0x3e4/0x790 fs/ext4/inode.c:6087
 ext4_evict_inode+0xb58/0x1270 fs/ext4/inode.c:279
 evict+0x3c8/0x810 fs/inode.c:705
 iput_final fs/inode.c:1834 [inline]
 iput+0x764/0x7f4 fs/inode.c:1860
 ext4_process_orphan+0x240/0x2b4 fs/ext4/orphan.c:360
 ext4_orphan_cleanup+0x908/0x104c fs/ext4/orphan.c:474
 __ext4_fill_super fs/ext4/super.c:5537 [inline]
 ext4_fill_super+0x6920/0x6e34 fs/ext4/super.c:5668
 get_tree_bdev+0x358/0x544 fs/super.c:1366
 ext4_get_tree+0x28/0x38 fs/ext4/super.c:5698
 vfs_get_tree+0x90/0x274 fs/super.c:1573
 do_new_mount+0x228/0x810 fs/namespace.c:3069
 path_mount+0x5b4/0xe78 fs/namespace.c:3399
 do_mount fs/namespace.c:3412 [inline]
 __do_sys_mount fs/namespace.c:3620 [inline]
 __se_sys_mount fs/namespace.c:3597 [inline]
 __arm64_sys_mount+0x49c/0x584 fs/namespace.c:3597
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x138 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585
irq event stamp: 5499
hardirqs last  enabled at (5499): [<ffff800011a43014>] __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:151 [inline]
hardirqs last  enabled at (5499): [<ffff800011a43014>] _raw_spin_unlock_irqrestore+0x48/0xac kernel/locking/spinlock.c:194
hardirqs last disabled at (5498): [<ffff800011a42e30>] __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:108 [inline]
hardirqs last disabled at (5498): [<ffff800011a42e30>] _raw_spin_lock_irqsave+0xa4/0xb4 kernel/locking/spinlock.c:162
softirqs last  enabled at (4232): [<ffff80000803092c>] local_bh_enable+0x10/0x34 include/linux/bottom_half.h:32
softirqs last disabled at (4230): [<ffff8000080308f8>] local_bh_disable+0x10/0x34 include/linux/bottom_half.h:19
---[ end trace 0000000000000000 ]---
EXT4-fs (loop0): 1 orphan inode deleted
EXT4-fs (loop0): mounted filesystem without journal. Quota mode: none.

Crashes (10):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/09/13 03:53 linux-6.1.y 3db754f56897 e2beed91 .config console log report syz / log [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-6-1-kasan-arm64 possible deadlock in ext4_writepages
2025/09/12 08:58 linux-6.1.y 3db754f56897 e2beed91 .config console log report syz / log [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-6-1-kasan-arm64 possible deadlock in ext4_writepages
2025/09/12 08:40 linux-6.1.y 3db754f56897 e2beed91 .config console log report syz / log [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-6-1-kasan-arm64 possible deadlock in ext4_writepages
2025/09/10 22:58 linux-6.1.y f97f1002271b fdeaa69b .config console log report syz / log [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-6-1-kasan-arm64 possible deadlock in ext4_writepages
2025/09/10 22:38 linux-6.1.y f97f1002271b fdeaa69b .config console log report syz / log [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-6-1-kasan-arm64 possible deadlock in ext4_writepages
2025/09/13 05:12 linux-6.1.y 3db754f56897 e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan possible deadlock in ext4_writepages
2025/09/13 03:40 linux-6.1.y 3db754f56897 e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 possible deadlock in ext4_writepages
2025/09/12 05:31 linux-6.1.y 3db754f56897 e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 possible deadlock in ext4_writepages
2025/09/12 05:31 linux-6.1.y 3db754f56897 e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 possible deadlock in ext4_writepages
2025/09/10 22:17 linux-6.1.y f97f1002271b fdeaa69b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 possible deadlock in ext4_writepages
* Struck through repros no longer work on HEAD.