syzbot

EXT4-fs error (device loop0): ext4_mb_generate_buddy:1126: group 0, block bitmap and bg descriptor inconsistent: 25 vs 1305 free clusters
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.19/4520 is trying to acquire lock:
ffff0000e5bc6518 (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_lock_xattr fs/ext4/xattr.h:158 [inline]
ffff0000e5bc6518 (&ei->xattr_sem){++++}-{3:3}, at: ext4_destroy_inline_data+0x30/0x114 fs/ext4/inline.c:1922

but task is already holding lock:
ffff0000d638ec18 (&sbi->s_writepages_rwsem){.+.+}-{0:0}, at: ext4_writepages+0x1b8/0x28b4 fs/ext4/inode.c:2717

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+0x70/0x2a8 include/linux/percpu-rwsem.h:51
       ext4_writepages+0x1b8/0x28b4 fs/ext4/inode.c:2717
       do_writepages+0x2b0/0x504 mm/page-writeback.c:2491
       __writeback_single_inode+0x164/0x1554 fs/fs-writeback.c:1622
       writeback_single_inode+0x1cc/0x740 fs/fs-writeback.c:1743
       write_inode_now+0x150/0x1cc fs/fs-writeback.c:2786
       iput_final fs/inode.c:1821 [inline]
       iput+0x5bc/0x7e4 fs/inode.c:1860
       ext4_xattr_block_set+0x1e9c/0x2880 fs/ext4/xattr.c:2093
       ext4_xattr_move_to_block fs/ext4/xattr.c:2611 [inline]
       ext4_xattr_make_inode_space fs/ext4/xattr.c:2686 [inline]
       ext4_expand_extra_isize_ea+0xe5c/0x17ac fs/ext4/xattr.c:2774
       __ext4_expand_extra_isize+0x298/0x358 fs/ext4/inode.c:6003
       ext4_try_to_expand_extra_isize fs/ext4/inode.c:6046 [inline]
       __ext4_mark_inode_dirty+0x3e4/0x784 fs/ext4/inode.c:6124
       ext4_evict_inode+0xb64/0x1278 fs/ext4/inode.c:281
       evict+0x3e0/0x828 fs/inode.c:705
       iput_final fs/inode.c:1834 [inline]
       iput+0x754/0x7e4 fs/inode.c:1860
       ext4_process_orphan+0x240/0x2b4 fs/ext4/orphan.c:358
       ext4_orphan_cleanup+0x920/0x1060 fs/ext4/orphan.c:472
       __ext4_fill_super fs/ext4/super.c:5574 [inline]
       ext4_fill_super+0x594c/0x61b0 fs/ext4/super.c:5693
       get_tree_bdev+0x358/0x544 fs/super.c:1366
       ext4_get_tree+0x28/0x38 fs/ext4/super.c:5723
       vfs_get_tree+0x90/0x274 fs/super.c:1573
       do_new_mount+0x228/0x810 fs/namespace.c:3078
       path_mount+0x5bc/0xe80 fs/namespace.c:3408
       do_mount fs/namespace.c:3421 [inline]
       __do_sys_mount fs/namespace.c:3629 [inline]
       __se_sys_mount fs/namespace.c:3606 [inline]
       __arm64_sys_mount+0x49c/0x59c fs/namespace.c:3606
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x130 arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x128 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

-> #0 (&ei->xattr_sem){++++}-{3:3}:
       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+0x2880/0x6800 kernel/locking/lockdep.c:5049
       lock_acquire+0x20c/0x63c kernel/locking/lockdep.c:5662
       down_write+0x5c/0x88 kernel/locking/rwsem.c:1573
       ext4_write_lock_xattr fs/ext4/xattr.h:158 [inline]
       ext4_destroy_inline_data+0x30/0x114 fs/ext4/inline.c:1922
       ext4_writepages+0x430/0x28b4 fs/ext4/inode.c:2763
       do_writepages+0x2b0/0x504 mm/page-writeback.c:2491
       filemap_fdatawrite_wbc+0x124/0x174 mm/filemap.c:388
       __filemap_fdatawrite_range mm/filemap.c:421 [inline]
       file_write_and_wait_range+0x11c/0x1f4 mm/filemap.c:774
       ext4_sync_file+0x210/0xc70 fs/ext4/fsync.c:151
       vfs_fsync_range+0x168/0x188 fs/sync.c:188
       generic_write_sync include/linux/fs.h:2962 [inline]
       ext4_buffered_write_iter+0x47c/0x528 fs/ext4/file.c:292
       ext4_file_write_iter+0x18c/0x1574 fs/ext4/file.c:-1
       call_write_iter include/linux/fs.h:2265 [inline]
       new_sync_write fs/read_write.c:491 [inline]
       vfs_write+0x3ec/0x7f0 fs/read_write.c:584
       ksys_write+0x12c/0x224 fs/read_write.c:637
       __do_sys_write fs/read_write.c:649 [inline]
       __se_sys_write fs/read_write.c:646 [inline]
       __arm64_sys_write+0x7c/0x90 fs/read_write.c:646
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x130 arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x128 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:

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

2 locks held by syz.0.19/4520:
 #0: ffff0000d638c460 (sb_writers#3){.+.+}-{0:0}, at: vfs_write+0x244/0x7f0 fs/read_write.c:580
 #1: ffff0000d638ec18 (&sbi->s_writepages_rwsem){.+.+}-{0:0}, at: ext4_writepages+0x1b8/0x28b4 fs/ext4/inode.c:2717

stack backtrace:
CPU: 0 PID: 4520 Comm: syz.0.19 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call trace:
 dump_backtrace+0x1c0/0x1ec 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+0xf4/0x15c 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+0x264/0x2f8 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+0x2880/0x6800 kernel/locking/lockdep.c:5049
 lock_acquire+0x20c/0x63c kernel/locking/lockdep.c:5662
 down_write+0x5c/0x88 kernel/locking/rwsem.c:1573
 ext4_write_lock_xattr fs/ext4/xattr.h:158 [inline]
 ext4_destroy_inline_data+0x30/0x114 fs/ext4/inline.c:1922
 ext4_writepages+0x430/0x28b4 fs/ext4/inode.c:2763
 do_writepages+0x2b0/0x504 mm/page-writeback.c:2491
 filemap_fdatawrite_wbc+0x124/0x174 mm/filemap.c:388
 __filemap_fdatawrite_range mm/filemap.c:421 [inline]
 file_write_and_wait_range+0x11c/0x1f4 mm/filemap.c:774
 ext4_sync_file+0x210/0xc70 fs/ext4/fsync.c:151
 vfs_fsync_range+0x168/0x188 fs/sync.c:188
 generic_write_sync include/linux/fs.h:2962 [inline]
 ext4_buffered_write_iter+0x47c/0x528 fs/ext4/file.c:292
 ext4_file_write_iter+0x18c/0x1574 fs/ext4/file.c:-1
 call_write_iter include/linux/fs.h:2265 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x3ec/0x7f0 fs/read_write.c:584
 ksys_write+0x12c/0x224 fs/read_write.c:637
 __do_sys_write fs/read_write.c:649 [inline]
 __se_sys_write fs/read_write.c:646 [inline]
 __arm64_sys_write+0x7c/0x90 fs/read_write.c:646
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x58/0x130 arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x128 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
EXT4-fs (loop0): Delayed block allocation failed for inode 15 at logical offset 0 with max blocks 1 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=20480
EXT4-fs (loop0): dirty_blocks=16
EXT4-fs (loop0): Block reservation details
EXT4-fs (loop0): i_reserved_data_blocks=1