Re: [syzbot] [ext4?] possible deadlock in ext4_destroy_inline_data (2)

syzbot
2025-12-01T06:21:21Z

syzbot has found a reproducer for the following issue on:

HEAD commit: 7d31f578f323 Add linux-next specific files for 20251128
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1209f912580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6336d8e94a7c517d
dashboard link: https://syzkaller.appspot.com/bug?extid=bb2455d02bda0b5701e3
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1442c192580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=108802b4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/6b49d8ad90de/disk-7d31f578.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/dbe2d4988ca7/vmlinux-7d31f578.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fc0448ab2411/bzImage-7d31f578.xz
mounted in repro #1: https://storage.googleapis.com/syzbot-assets/c224e4ae2f71/mount_0.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=16b5c512580000)
mounted in repro #2: https://storage.googleapis.com/syzbot-assets/6a86b64b703d/mount_1.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=170802b4580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+bb2455d02bda0b5701e3@syzkaller.appspotmail.com

EXT4-fs: Ignoring removed bh option
EXT4-fs (loop0): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: none.
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.28/6033 is trying to acquire lock:
ffff88805e5deaa8 (&ei->xattr_sem){++++}-{4:4}, at: ext4_write_lock_xattr fs/ext4/xattr.h:157 [inline]
ffff88805e5deaa8 (&ei->xattr_sem){++++}-{4:4}, at: ext4_destroy_inline_data+0x28/0xe0 fs/ext4/inline.c:1797

but task is already holding lock:
ffff8880347c0b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
ffff8880347c0b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages_down_read fs/ext4/ext4.h:1820 [inline]
ffff8880347c0b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages+0x1ca/0x350 fs/ext4/inode.c:3025

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&sbi->s_writepages_rwsem){++++}-{0:0}:
percpu_down_read_internal+0x48/0x1c0 include/linux/percpu-rwsem.h:53
percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
ext4_writepages_down_read fs/ext4/ext4.h:1820 [inline]
ext4_writepages+0x1ca/0x350 fs/ext4/inode.c:3025
do_writepages+0x32e/0x550 mm/page-writeback.c:2598
__writeback_single_inode+0x133/0x1240 fs/fs-writeback.c:1737
writeback_single_inode+0x493/0xc70 fs/fs-writeback.c:1858
write_inode_now+0x160/0x1d0 fs/fs-writeback.c:2924
iput_final fs/inode.c:1941 [inline]
iput+0xa77/0x1030 fs/inode.c:2003
ext4_xattr_block_set+0x1fce/0x2ac0 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+0x12da/0x1ea0 fs/ext4/xattr.c:2831
__ext4_expand_extra_isize+0x30d/0x400 fs/ext4/inode.c:6349
ext4_try_to_expand_extra_isize fs/ext4/inode.c:6392 [inline]
__ext4_mark_inode_dirty+0x45c/0x6e0 fs/ext4/inode.c:6470
ext4_evict_inode+0x79c/0xe60 fs/ext4/inode.c:253
evict+0x5f4/0xae0 fs/inode.c:837
ext4_orphan_cleanup+0xc20/0x1460 fs/ext4/orphan.c:472
__ext4_fill_super fs/ext4/super.c:5658 [inline]
ext4_fill_super+0x58a1/0x6160 fs/ext4/super.c:5777
get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1691
vfs_get_tree+0x92/0x2a0 fs/super.c:1751
fc_mount fs/namespace.c:1209 [inline]
do_new_mount_fc fs/namespace.c:3646 [inline]
do_new_mount+0x302/0xa10 fs/namespace.c:3722
do_mount fs/namespace.c:4045 [inline]
__do_sys_mount fs/namespace.c:4234 [inline]
__se_sys_mount+0x313/0x410 fs/namespace.c:4211
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&ei->xattr_sem){++++}-{4:4}:
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+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868
down_write+0x96/0x1f0 kernel/locking/rwsem.c:1590
ext4_write_lock_xattr fs/ext4/xattr.h:157 [inline]
ext4_destroy_inline_data+0x28/0xe0 fs/ext4/inline.c:1797
ext4_do_writepages+0x4e6/0x4500 fs/ext4/inode.c:2811
ext4_writepages+0x203/0x350 fs/ext4/inode.c:3026
do_writepages+0x32e/0x550 mm/page-writeback.c:2598
filemap_writeback mm/filemap.c:387 [inline]
filemap_fdatawrite_range mm/filemap.c:412 [inline]
file_write_and_wait_range+0x23e/0x340 mm/filemap.c:786
generic_buffers_fsync_noflush+0x70/0x1d0 fs/buffer.c:609
ext4_fsync_nojournal fs/ext4/fsync.c:88 [inline]
ext4_sync_file+0x322/0xae0 fs/ext4/fsync.c:147
generic_write_sync include/linux/fs.h:2616 [inline]
ext4_buffered_write_iter+0x2ca/0x3a0 fs/ext4/file.c:305
ext4_file_write_iter+0x292/0x1bc0 fs/ext4/file.c:-1
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x5c9/0xb30 fs/read_write.c:686
ksys_pwrite64 fs/read_write.c:793 [inline]
__do_sys_pwrite64 fs/read_write.c:801 [inline]
__se_sys_pwrite64 fs/read_write.c:798 [inline]
__x64_sys_pwrite64+0x193/0x220 fs/read_write.c:798
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
rlock(&sbi->s_writepages_rwsem);
lock(&ei->xattr_sem);
lock(&sbi->s_writepages_rwsem);
lock(&ei->xattr_sem);

*** DEADLOCK ***

2 locks held by syz.0.28/6033:
#0: ffff8880347c2420 (sb_writers#4){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2681 [inline]
#0: ffff8880347c2420 (sb_writers#4){.+.+}-{0:0}, at: vfs_write+0x211/0xb30 fs/read_write.c:682
#1: ffff8880347c0b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
#1: ffff8880347c0b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages_down_read fs/ext4/ext4.h:1820 [inline]
#1: ffff8880347c0b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages+0x1ca/0x350 fs/ext4/inode.c:3025

stack backtrace:
CPU: 1 UID: 0 PID: 6033 Comm: syz.0.28 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_lvl+0x189/0x250 lib/dump_stack.c:120
print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2043
check_noncircular+0x12e/0x150 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+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868
down_write+0x96/0x1f0 kernel/locking/rwsem.c:1590
ext4_write_lock_xattr fs/ext4/xattr.h:157 [inline]
ext4_destroy_inline_data+0x28/0xe0 fs/ext4/inline.c:1797
ext4_do_writepages+0x4e6/0x4500 fs/ext4/inode.c:2811
ext4_writepages+0x203/0x350 fs/ext4/inode.c:3026
do_writepages+0x32e/0x550 mm/page-writeback.c:2598
filemap_writeback mm/filemap.c:387 [inline]
filemap_fdatawrite_range mm/filemap.c:412 [inline]
file_write_and_wait_range+0x23e/0x340 mm/filemap.c:786
generic_buffers_fsync_noflush+0x70/0x1d0 fs/buffer.c:609
ext4_fsync_nojournal fs/ext4/fsync.c:88 [inline]
ext4_sync_file+0x322/0xae0 fs/ext4/fsync.c:147
generic_write_sync include/linux/fs.h:2616 [inline]
ext4_buffered_write_iter+0x2ca/0x3a0 fs/ext4/file.c:305
ext4_file_write_iter+0x292/0x1bc0 fs/ext4/file.c:-1
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x5c9/0xb30 fs/read_write.c:686
ksys_pwrite64 fs/read_write.c:793 [inline]
__do_sys_pwrite64 fs/read_write.c:801 [inline]
__se_sys_pwrite64 fs/read_write.c:798 [inline]
__x64_sys_pwrite64+0x193/0x220 fs/read_write.c:798
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2eec38f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 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:00007fff228a92f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007f2eec5e5fa0 RCX: 00007f2eec38f749
RDX: 000000000000fdef RSI: 0000200000000140 RDI: 0000000000000004
RBP: 00007f2eec413f91 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000fecc R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2eec5e5fa0 R14: 00007f2eec5e5fa0 R15: 0000000000000004
</TASK>
EXT4-fs error (device loop0): ext4_mb_generate_buddy:1306: group 0, block bitmap and bg descriptor inconsistent: 25 vs 150994969 free clusters
EXT4-fs (loop0): Delayed block allocation failed for inode 15 at logical offset 31 with max blocks 33 with error 28
EXT4-fs (loop0): This should not happen!! Data will be lost

EXT4-fs (loop0): Total free blocks count 0
EXT4-fs (loop0): Free/Dirty block details
EXT4-fs (loop0): free_blocks=2415919104
EXT4-fs (loop0): dirty_blocks=64
EXT4-fs (loop0): Block reservation details
EXT4-fs (loop0): i_reserved_data_blocks=4

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