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Date:   Mon, 09 Aug 2021 10:43:05 -0700
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Subject: Re: [syzbot] possible deadlock in dquot_commit
From:   syzbot <syzbot+3b6f9218b1301ddda3e2@syzkaller.appspotmail.com>
To:     dvyukov@google.com, jack@suse.com, jack@suse.cz,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
        syzkaller@googlegroups.com, tytso@mit.edu
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Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
possible deadlock in dquot_commit

EXT4-fs warning (device loop4): ext4_enable_quotas:6478: Failed to enable quota tracking (type=1, err=-22). Please run e2fsck to fix.
EXT4-fs (loop4): mount failed
======================================================
WARNING: possible circular locking dependency detected
5.14.0-rc4-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.4/28771 is trying to acquire lock:
ffff88803941cea8 (&dquot->dq_lock){+.+.}-{3:3}, at: dquot_commit+0x57/0x360 fs/quota/dquot.c:474

but task is already holding lock:
ffff8880463d2a58 (&ei->i_data_sem/2){++++}-{3:3}, at: ext4_map_blocks+0x9e5/0x1cb0 fs/ext4/inode.c:631

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&ei->i_data_sem/2){++++}-{3:3}:
       lock_acquire+0x182/0x4a0 kernel/locking/lockdep.c:5625
       down_read+0x3b/0x50 kernel/locking/rwsem.c:1353
       ext4_map_blocks+0x266/0x1cb0 fs/ext4/inode.c:561
       ext4_getblk+0x187/0x6c0 fs/ext4/inode.c:848
       ext4_bread+0x2a/0x170 fs/ext4/inode.c:900
       ext4_quota_write+0x2c7/0x5b0 fs/ext4/super.c:6602
       write_blk fs/quota/quota_tree.c:64 [inline]
       get_free_dqblk+0x33a/0x660 fs/quota/quota_tree.c:93
       do_insert_tree+0x24c/0x1d30 fs/quota/quota_tree.c:300
       do_insert_tree+0x659/0x1d30 fs/quota/quota_tree.c:331
       do_insert_tree+0x659/0x1d30 fs/quota/quota_tree.c:331
       do_insert_tree+0x659/0x1d30 fs/quota/quota_tree.c:331
       dq_insert_tree fs/quota/quota_tree.c:357 [inline]
       qtree_write_dquot+0x3b6/0x530 fs/quota/quota_tree.c:376
       v2_write_dquot+0x110/0x1a0 fs/quota/quota_v2.c:358
       dquot_acquire+0x2d7/0x5b0 fs/quota/dquot.c:441
       ext4_acquire_dquot+0x2e0/0x400 fs/ext4/super.c:6261
       dqget+0x999/0xdc0 fs/quota/dquot.c:899
       __dquot_initialize+0x291/0xd40 fs/quota/dquot.c:1477
       ext4_create+0xb0/0x550 fs/ext4/namei.c:2731
       lookup_open fs/namei.c:3228 [inline]
       open_last_lookups fs/namei.c:3298 [inline]
       path_openat+0x13b7/0x36b0 fs/namei.c:3504
       do_filp_open+0x253/0x4d0 fs/namei.c:3534
       do_sys_openat2+0x124/0x460 fs/open.c:1204
       do_sys_open fs/open.c:1220 [inline]
       __do_sys_creat fs/open.c:1294 [inline]
       __se_sys_creat fs/open.c:1288 [inline]
       __x64_sys_creat+0x11f/0x160 fs/open.c:1288
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #1 (&s->s_dquot.dqio_sem){++++}-{3:3}:
       lock_acquire+0x182/0x4a0 kernel/locking/lockdep.c:5625
       down_read+0x3b/0x50 kernel/locking/rwsem.c:1353
       v2_read_dquot+0x4a/0x100 fs/quota/quota_v2.c:332
       dquot_acquire+0x144/0x5b0 fs/quota/dquot.c:432
       ext4_acquire_dquot+0x2e0/0x400 fs/ext4/super.c:6261
       dqget+0x999/0xdc0 fs/quota/dquot.c:899
       __dquot_initialize+0x291/0xd40 fs/quota/dquot.c:1477
       ext4_create+0xb0/0x550 fs/ext4/namei.c:2731
       lookup_open fs/namei.c:3228 [inline]
       open_last_lookups fs/namei.c:3298 [inline]
       path_openat+0x13b7/0x36b0 fs/namei.c:3504
       do_filp_open+0x253/0x4d0 fs/namei.c:3534
       do_sys_openat2+0x124/0x460 fs/open.c:1204
       do_sys_open fs/open.c:1220 [inline]
       __do_sys_creat fs/open.c:1294 [inline]
       __se_sys_creat fs/open.c:1288 [inline]
       __x64_sys_creat+0x11f/0x160 fs/open.c:1288
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #0 (&dquot->dq_lock){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3051 [inline]
       check_prevs_add+0x4f9/0x5b30 kernel/locking/lockdep.c:3174
       __lo


Tested on:

commit:         902e7f37 Merge tag 'net-5.14-rc5' of git://git.kernel...
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=125d6b79300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=702bfdfbf389c324
dashboard link: https://syzkaller.appspot.com/bug?extid=3b6f9218b1301ddda3e2
compiler:       Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.1
patch:          https://syzkaller.appspot.com/x/patch.diff?x=173c0ee9300000