syzbot

loop0: detected capacity change from 0 to 512
ext4 filesystem being mounted at /96/file2 supports timestamps until 2038-01-19 (0x7fffffff)
======================================================
WARNING: possible circular locking dependency detected
6.1.148-syzkaller #0 Not tainted
------------------------------------------------------
syz.0.113/4620 is trying to acquire lock:
ffff888068f9a268 (&dquot->dq_lock){+.+.}-{3:3}, at: dquot_commit+0x5a/0x410 fs/quota/dquot.c:507

but task is already holding lock:
ffff888068eb9698 (&ei->i_data_sem/2){++++}-{3:3}, at: ext4_map_blocks+0x903/0x1b60 fs/ext4/inode.c:672

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&ei->i_data_sem/2){++++}-{3:3}:
       down_write+0x36/0x60 kernel/locking/rwsem.c:1573
       ext4_map_blocks+0x903/0x1b60 fs/ext4/inode.c:672
       ext4_getblk+0x1ab/0x6d0 fs/ext4/inode.c:890
       ext4_bread+0x26/0x170 fs/ext4/inode.c:946
       ext4_quota_write+0x230/0x570 fs/ext4/super.c:7201
       write_blk fs/quota/quota_tree.c:70 [inline]
       find_free_dqentry+0x673/0xc20 fs/quota/quota_tree.c:318
       do_insert_tree+0x70d/0x1040 fs/quota/quota_tree.c:400
       do_insert_tree+0x9ae/0x1040 fs/quota/quota_tree.c:402
       do_insert_tree+0x9ae/0x1040 fs/quota/quota_tree.c:402
       do_insert_tree+0x9ae/0x1040 fs/quota/quota_tree.c:402
       dq_insert_tree fs/quota/quota_tree.c:432 [inline]
       qtree_write_dquot+0x48d/0x5b0 fs/quota/quota_tree.c:451
       v2_write_dquot+0x108/0x190 fs/quota/quota_v2.c:361
       dquot_acquire+0x2d5/0x520 fs/quota/dquot.c:472
       ext4_acquire_dquot+0x2d9/0x4a0 fs/ext4/super.c:6810
       dqget+0x778/0xeb0 fs/quota/dquot.c:988
       __dquot_initialize+0x328/0xcb0 fs/quota/dquot.c:1517
       ext4_file_open+0x2cb/0x6a0 fs/ext4/file.c:872
       do_dentry_open+0x7e9/0x10d0 fs/open.c:882
       do_open fs/namei.c:3626 [inline]
       path_openat+0x25c6/0x2e70 fs/namei.c:3783
       do_filp_open+0x1c1/0x3c0 fs/namei.c:3810
       do_sys_openat2+0x142/0x490 fs/open.c:1318
       do_sys_open fs/open.c:1334 [inline]
       __do_sys_openat fs/open.c:1350 [inline]
       __se_sys_openat fs/open.c:1345 [inline]
       __x64_sys_openat+0x135/0x160 fs/open.c:1345
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #1 (&s->s_dquot.dqio_sem){++++}-{3:3}:
       down_read+0x42/0x2d0 kernel/locking/rwsem.c:1520
       v2_read_dquot+0x4a/0x110 fs/quota/quota_v2.c:335
       dquot_acquire+0x152/0x520 fs/quota/dquot.c:463
       ext4_acquire_dquot+0x2d9/0x4a0 fs/ext4/super.c:6810
       dqget+0x778/0xeb0 fs/quota/dquot.c:988
       __dquot_initialize+0x328/0xcb0 fs/quota/dquot.c:1517
       ext4_file_open+0x2cb/0x6a0 fs/ext4/file.c:872
       do_dentry_open+0x7e9/0x10d0 fs/open.c:882
       do_open fs/namei.c:3626 [inline]
       path_openat+0x25c6/0x2e70 fs/namei.c:3783
       do_filp_open+0x1c1/0x3c0 fs/namei.c:3810
       do_sys_openat2+0x142/0x490 fs/open.c:1318
       do_sys_open fs/open.c:1334 [inline]
       __do_sys_openat fs/open.c:1350 [inline]
       __se_sys_openat fs/open.c:1345 [inline]
       __x64_sys_openat+0x135/0x160 fs/open.c:1345
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #0 (&dquot->dq_lock){+.+.}-{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+0x2cf8/0x7c50 kernel/locking/lockdep.c:5049
       lock_acquire+0x1b4/0x490 kernel/locking/lockdep.c:5662
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x120/0xaf0 kernel/locking/mutex.c:747
       dquot_commit+0x5a/0x410 fs/quota/dquot.c:507
       ext4_write_dquot+0x1f0/0x360 fs/ext4/super.c:6790
       mark_dquot_dirty fs/quota/dquot.c:372 [inline]
       mark_all_dquot_dirty+0x1e3/0x400 fs/quota/dquot.c:412
       __dquot_alloc_space+0x5fc/0xe60 fs/quota/dquot.c:1752
       dquot_alloc_space_nodirty include/linux/quotaops.h:300 [inline]
       dquot_alloc_space include/linux/quotaops.h:313 [inline]
       dquot_alloc_block include/linux/quotaops.h:337 [inline]
       ext4_mb_new_blocks+0xf74/0x4720 fs/ext4/mballoc.c:5727
       ext4_ext_map_blocks+0x143c/0x66d0 fs/ext4/extents.c:4340
       ext4_map_blocks+0x9d1/0x1b60 fs/ext4/inode.c:679
       _ext4_get_block+0x1d7/0x4e0 fs/ext4/inode.c:822
       ext4_block_write_begin+0x637/0x12f0 fs/ext4/inode.c:1124
       ext4_write_begin+0x624/0xf50 fs/ext4/ext4_jbd2.h:-1
       generic_perform_write+0x2db/0x560 mm/filemap.c:3846
       ext4_buffered_write_iter+0x11a/0x3e0 fs/ext4/file.c:285
       ext4_file_write_iter+0x1d6/0x16e0 fs/ext4/file.c:-1
       do_iter_readv_writev fs/read_write.c:-1 [inline]
       do_iter_write+0x62d/0xaf0 fs/read_write.c:861
       vfs_writev fs/read_write.c:934 [inline]
       do_pwritev+0x201/0x340 fs/read_write.c:1031
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

other info that might help us debug this:

Chain exists of:
  &dquot->dq_lock --> &s->s_dquot.dqio_sem --> &ei->i_data_sem/2

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&ei->i_data_sem/2);
                               lock(&s->s_dquot.dqio_sem);
                               lock(&ei->i_data_sem/2);
  lock(&dquot->dq_lock);

 *** DEADLOCK ***

4 locks held by syz.0.113/4620:
 #0: ffff88805be10460 (sb_writers#4){.+.+}-{0:0}, at: vfs_writev fs/read_write.c:933 [inline]
 #0: ffff88805be10460 (sb_writers#4){.+.+}-{0:0}, at: do_pwritev+0x1ef/0x340 fs/read_write.c:1031
 #1: ffff888068eb9810 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: inode_lock include/linux/fs.h:758 [inline]
 #1: ffff888068eb9810 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: ext4_buffered_write_iter+0xa1/0x3e0 fs/ext4/file.c:279
 #2: ffff888068eb9698 (&ei->i_data_sem/2){++++}-{3:3}, at: ext4_map_blocks+0x903/0x1b60 fs/ext4/inode.c:672
 #3: ffffffff8cc73048 (dquot_srcu){....}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
 #3: ffffffff8cc73048 (dquot_srcu){....}-{0:0}, at: srcu_read_lock include/linux/srcu.h:165 [inline]
 #3: ffffffff8cc73048 (dquot_srcu){....}-{0:0}, at: __dquot_alloc_space+0x173/0xe60 fs/quota/dquot.c:1716

stack backtrace:
CPU: 1 PID: 4620 Comm: syz.0.113 Not tainted 6.1.148-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x22e lib/dump_stack.c:106
 check_noncircular+0x274/0x310 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+0x2cf8/0x7c50 kernel/locking/lockdep.c:5049
 lock_acquire+0x1b4/0x490 kernel/locking/lockdep.c:5662
 __mutex_lock_common kernel/locking/mutex.c:603 [inline]
 __mutex_lock+0x120/0xaf0 kernel/locking/mutex.c:747
 dquot_commit+0x5a/0x410 fs/quota/dquot.c:507
 ext4_write_dquot+0x1f0/0x360 fs/ext4/super.c:6790
 mark_dquot_dirty fs/quota/dquot.c:372 [inline]
 mark_all_dquot_dirty+0x1e3/0x400 fs/quota/dquot.c:412
 __dquot_alloc_space+0x5fc/0xe60 fs/quota/dquot.c:1752
 dquot_alloc_space_nodirty include/linux/quotaops.h:300 [inline]
 dquot_alloc_space include/linux/quotaops.h:313 [inline]
 dquot_alloc_block include/linux/quotaops.h:337 [inline]
 ext4_mb_new_blocks+0xf74/0x4720 fs/ext4/mballoc.c:5727
 ext4_ext_map_blocks+0x143c/0x66d0 fs/ext4/extents.c:4340
 ext4_map_blocks+0x9d1/0x1b60 fs/ext4/inode.c:679
 _ext4_get_block+0x1d7/0x4e0 fs/ext4/inode.c:822
 ext4_block_write_begin+0x637/0x12f0 fs/ext4/inode.c:1124
 ext4_write_begin+0x624/0xf50 fs/ext4/ext4_jbd2.h:-1
 generic_perform_write+0x2db/0x560 mm/filemap.c:3846
 ext4_buffered_write_iter+0x11a/0x3e0 fs/ext4/file.c:285
 ext4_file_write_iter+0x1d6/0x16e0 fs/ext4/file.c:-1
 do_iter_readv_writev fs/read_write.c:-1 [inline]
 do_iter_write+0x62d/0xaf0 fs/read_write.c:861
 vfs_writev fs/read_write.c:934 [inline]
 do_pwritev+0x201/0x340 fs/read_write.c:1031
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fde55d8ebe9
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:00007fffbedcbfa8 EFLAGS: 00000246 ORIG_RAX: 0000000000000148
RAX: ffffffffffffffda RBX: 00007fde55fb5fa0 RCX: 00007fde55d8ebe9
RDX: 0000000000000001 RSI: 00002000000001c0 RDI: 0000000000000004
RBP: 00007fde55e11e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000e7b R11: 0000000000000246 R12: 0000000000000000
R13: 00007fde55fb5fa0 R14: 00007fde55fb5fa0 R15: 0000000000000006
 </TASK>