[syzbot] possible deadlock in ext4_bmap

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ca688bff68bc Add linux-next specific files for 20220808
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=177eb001080000
kernel config: https://syzkaller.appspot.com/x/.config?x=4c20e006003cdecb
dashboard link: https://syzkaller.appspot.com/bug?extid=9543479984ae9e576000
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+954347...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
5.19.0-next-20220808-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.3/15950 is trying to acquire lock:
ffff88801b348400 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: inode_lock_shared include/linux/fs.h:771 [inline]
ffff88801b348400 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: ext4_bmap+0x4e/0x460 fs/ext4/inode.c:3157

but task is already holding lock:
ffff88814bede3f8 (&journal->j_checkpoint_mutex){+.+.}-{3:3}, at: jbd2_journal_flush+0x487/0xc00 fs/jbd2/journal.c:2472

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&journal->j_checkpoint_mutex){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
mutex_lock_io_nested+0x13f/0x1190 kernel/locking/mutex.c:833
__jbd2_log_wait_for_space+0x234/0x460 fs/jbd2/checkpoint.c:110
add_transaction_credits+0xa2d/0xb70 fs/jbd2/transaction.c:298
start_this_handle+0x3ae/0x14a0 fs/jbd2/transaction.c:422
jbd2__journal_start+0x38c/0x910 fs/jbd2/transaction.c:520
__ext4_journal_start_sb+0x3a3/0x490 fs/ext4/ext4_jbd2.c:105
__ext4_journal_start fs/ext4/ext4_jbd2.h:326 [inline]
ext4_dirty_inode+0x9d/0x110 fs/ext4/inode.c:5963
__mark_inode_dirty+0x48b/0x1040 fs/fs-writeback.c:2381
mark_inode_dirty include/linux/fs.h:2467 [inline]
generic_write_end+0x350/0x440 fs/buffer.c:2199
ext4_da_write_end+0x16e/0x9a0 fs/ext4/inode.c:3089
generic_perform_write+0x306/0x560 mm/filemap.c:3749
ext4_buffered_write_iter+0x15b/0x460 fs/ext4/file.c:270
ext4_file_write_iter+0x44a/0x1660 fs/ext4/file.c:679
call_write_iter include/linux/fs.h:2192 [inline]
do_iter_readv_writev+0x20b/0x3b0 fs/read_write.c:729
do_iter_write+0x182/0x700 fs/read_write.c:855
vfs_iter_write+0x70/0xa0 fs/read_write.c:896
iter_file_splice_write+0x741/0xc90 fs/splice.c:686
do_splice_from fs/splice.c:764 [inline]
direct_splice_actor+0x110/0x180 fs/splice.c:931
splice_direct_to_actor+0x331/0x8a0 fs/splice.c:886
do_splice_direct+0x1a7/0x270 fs/splice.c:974
do_sendfile+0xb19/0x1270 fs/read_write.c:1249
__do_sys_sendfile64 fs/read_write.c:1311 [inline]
__se_sys_sendfile64 fs/read_write.c:1303 [inline]
__x64_sys_sendfile64+0x149/0x210 fs/read_write.c:1303
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

-> #0 (&sb->s_type->i_mutex_key#8){++++}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3095 [inline]
check_prevs_add kernel/locking/lockdep.c:3214 [inline]
validate_chain kernel/locking/lockdep.c:3829 [inline]
__lock_acquire+0x2a43/0x56d0 kernel/locking/lockdep.c:5053
lock_acquire kernel/locking/lockdep.c:5666 [inline]
lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5631
down_read+0x98/0x450 kernel/locking/rwsem.c:1499
inode_lock_shared include/linux/fs.h:771 [inline]
ext4_bmap+0x4e/0x460 fs/ext4/inode.c:3157
bmap+0xaa/0x120 fs/inode.c:1799
jbd2_journal_bmap+0xa8/0x180 fs/jbd2/journal.c:971
__jbd2_journal_erase fs/jbd2/journal.c:1784 [inline]
jbd2_journal_flush+0x84f/0xc00 fs/jbd2/journal.c:2490
ext4_ioctl_checkpoint fs/ext4/ioctl.c:1082 [inline]
__ext4_ioctl+0x28fd/0x4ab0 fs/ext4/ioctl.c:1586
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl fs/ioctl.c:856 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&journal->j_checkpoint_mutex);
lock(&sb->s_type->i_mutex_key#8);
lock(&journal->j_checkpoint_mutex);
lock(&sb->s_type->i_mutex_key#8);

*** DEADLOCK ***

2 locks held by syz-executor.3/15950:
#0: ffff88814bede170 (&journal->j_barrier){+.+.}-{3:3}, at: jbd2_journal_lock_updates+0x15e/0x310 fs/jbd2/transaction.c:904
#1: ffff88814bede3f8 (&journal->j_checkpoint_mutex){+.+.}-{3:3}, at: jbd2_journal_flush+0x487/0xc00 fs/jbd2/journal.c:2472

stack backtrace:
CPU: 1 PID: 15950 Comm: syz-executor.3 Not tainted 5.19.0-next-20220808-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2175
check_prev_add kernel/locking/lockdep.c:3095 [inline]
check_prevs_add kernel/locking/lockdep.c:3214 [inline]
validate_chain kernel/locking/lockdep.c:3829 [inline]
__lock_acquire+0x2a43/0x56d0 kernel/locking/lockdep.c:5053
lock_acquire kernel/locking/lockdep.c:5666 [inline]
lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5631
down_read+0x98/0x450 kernel/locking/rwsem.c:1499
inode_lock_shared include/linux/fs.h:771 [inline]
ext4_bmap+0x4e/0x460 fs/ext4/inode.c:3157
bmap+0xaa/0x120 fs/inode.c:1799
jbd2_journal_bmap+0xa8/0x180 fs/jbd2/journal.c:971
__jbd2_journal_erase fs/jbd2/journal.c:1784 [inline]
jbd2_journal_flush+0x84f/0xc00 fs/jbd2/journal.c:2490
ext4_ioctl_checkpoint fs/ext4/ioctl.c:1082 [inline]
__ext4_ioctl+0x28fd/0x4ab0 fs/ext4/ioctl.c:1586
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl fs/ioctl.c:856 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7feb4e689279
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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007feb4f798168 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007feb4e79bf80 RCX: 00007feb4e689279
RDX: 0000000020000000 RSI: 000000004004662b RDI: 0000000000000005
RBP: 00007feb4e6e3189 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffc38bb538f R14: 00007feb4f798300 R15: 0000000000022000
</TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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syzbot will keep track of this issue. See:
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: ca688bff68bc Add linux-next specific files for 20220808
git tree: linux-next

console+strace: https://syzkaller.appspot.com/x/log.txt?x=15a71e71080000

kernel config: https://syzkaller.appspot.com/x/.config?x=4c20e006003cdecb
dashboard link: https://syzkaller.appspot.com/bug?extid=9543479984ae9e576000
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1551c53e080000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14fcdbfa080000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+954347...@syzkaller.appspotmail.com

warning: checkpointing journal with EXT4_IOC_CHECKPOINT_FLAG_ZEROOUT can be slow

======================================================
WARNING: possible circular locking dependency detected
5.19.0-next-20220808-syzkaller #0 Not tainted
------------------------------------------------------

syz-executor725/3607 is trying to acquire lock:
ffff888144c48400 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: inode_lock_shared include/linux/fs.h:771 [inline]
ffff888144c48400 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: ext4_bmap+0x4e/0x460 fs/ext4/inode.c:3157

but task is already holding lock:

ffff88807ec503f8 (&journal->j_checkpoint_mutex){+.+.}-{3:3}, at: jbd2_journal_flush+0x487/0xc00 fs/jbd2/journal.c:2472

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&journal->j_checkpoint_mutex){+.+.}-{3:3}:

__mutex_lock_common kernel/locking/mutex.c:603 [inline]
mutex_lock_io_nested+0x13f/0x1190 kernel/locking/mutex.c:833

jbd2_journal_flush+0x19a/0xc00 fs/jbd2/journal.c:2462

ext4_ioctl_checkpoint fs/ext4/ioctl.c:1082 [inline]
__ext4_ioctl+0x28fd/0x4ab0 fs/ext4/ioctl.c:1586
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl fs/ioctl.c:856 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

-> #2 (&journal->j_barrier){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x12f/0x1350 kernel/locking/mutex.c:747
jbd2_journal_lock_updates+0x15e/0x310 fs/jbd2/transaction.c:904
ext4_change_inode_journal_flag+0x180/0x530 fs/ext4/inode.c:6014
ext4_ioctl_setflags fs/ext4/ioctl.c:685 [inline]
ext4_fileattr_set+0xddf/0x1930 fs/ext4/ioctl.c:1001
vfs_fileattr_set+0x7f5/0xbe0 fs/ioctl.c:696
ioctl_fssetxattr fs/ioctl.c:758 [inline]
do_vfs_ioctl+0xe62/0x15c0 fs/ioctl.c:845
__do_sys_ioctl fs/ioctl.c:868 [inline]
__se_sys_ioctl fs/ioctl.c:856 [inline]
__x64_sys_ioctl+0x108/0x200 fs/ioctl.c:856

do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

-> #1 (&sbi->s_writepages_rwsem){++++}-{0:0}:
percpu_down_write+0x4d/0x440 kernel/locking/percpu-rwsem.c:221
ext4_ind_migrate+0x237/0x840 fs/ext4/migrate.c:624
ext4_ioctl_setflags fs/ext4/ioctl.c:694 [inline]
ext4_fileattr_set+0x14b8/0x1930 fs/ext4/ioctl.c:1001
vfs_fileattr_set+0x7f5/0xbe0 fs/ioctl.c:696
ioctl_fssetxattr fs/ioctl.c:758 [inline]
do_vfs_ioctl+0xe62/0x15c0 fs/ioctl.c:845
__do_sys_ioctl fs/ioctl.c:868 [inline]
__se_sys_ioctl fs/ioctl.c:856 [inline]
__x64_sys_ioctl+0x108/0x200 fs/ioctl.c:856

Chain exists of:
&sb->s_type->i_mutex_key#8 --> &journal->j_barrier --> &journal->j_checkpoint_mutex

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&journal->j_checkpoint_mutex);

lock(&journal->j_barrier);

lock(&journal->j_checkpoint_mutex);
lock(&sb->s_type->i_mutex_key#8);

*** DEADLOCK ***

2 locks held by syz-executor725/3607:
#0: ffff88807ec50170 (&journal->j_barrier){+.+.}-{3:3}, at: jbd2_journal_lock_updates+0x15e/0x310 fs/jbd2/transaction.c:904
#1: ffff88807ec503f8 (&journal->j_checkpoint_mutex){+.+.}-{3:3}, at: jbd2_journal_flush+0x487/0xc00 fs/jbd2/journal.c:2472

stack backtrace:
CPU: 1 PID: 3607 Comm: syz-executor725 Not tainted 5.19.0-next-20220808-syzkaller #0

RIP: 0033:0x7fe2d1101d69
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 b1 14 00 00 90 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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd7aba8f78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fe2d1101d69
RDX: 0000000020000000 RSI: 000000004004662b RDI: 0000000000000004
RBP: 0000000000000000 R08: 00007ffd7aba9118 R09: 00007ffd7aba9118
R10: 00007ffd7aba9118 R11: 0000000000000246 R12: 00007fe2d10c55f0
R13: 431bde82d7b634db R14: 0000000000000000 R15: 0000000000000000
</TASK>

[Hillf Danton]

On Mon, 08 Aug 2022 12:02:24 -0700

Break lock chain by replacing lock with trylock.

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git ca688bff68bc

--- a/fs/ext4/inode.c
+++ i/fs/ext4/inode.c
@@ -3154,7 +3154,8 @@ static sector_t ext4_bmap(struct address
sector_t ret = 0;
int err;

- inode_lock_shared(inode);
+ if (!inode_trylock_shared(inode))
+ return ret;
/*
* We can get here for an inline file via the FIBMAP ioctl
*/
--

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+954347...@syzkaller.appspotmail.com

Tested on:

commit: ca688bff Add linux-next specific files for 20220808
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
console output: https://syzkaller.appspot.com/x/log.txt?x=147eb8be080000

kernel config: https://syzkaller.appspot.com/x/.config?x=4c20e006003cdecb
dashboard link: https://syzkaller.appspot.com/bug?extid=9543479984ae9e576000
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

patch: https://syzkaller.appspot.com/x/patch.diff?x=17ee2476080000

Note: testing is done by a robot and is best-effort only.

[Jason Yan]

The inode_lock(inode) in vfs_fileattr_set() is a regular file inode and
inode_lock_shared(inode) in ext4_bmap() is a journal inode.

So this might be a false positive deadlock warning.

Thanks,
Jason

> .
>

[Eric Biggers]

I got this report while running syzkaller too. It's very annoying because
anyone running syzkaller will probably get this if the filesystem is ext4.

ext4_bmap() didn't use to take the inode lock. It started in this very recent
commit:

commit 51ae846cff568c8c29921b1b28eb2dfbcd4ac12d
Author: Ye Bin <yeb...@huawei.com>
Date: Fri Jun 17 09:39:35 2022 +0800

ext4: fix warning in ext4_iomap_begin as race between bmap and write

Ye, any thoughts on what to do about this?

- Eric

[Theodore Ts'o]

On Mon, Aug 08, 2022 at 12:33:22AM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: ca688bff68bc Add linux-next specific files for 20220808
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=177eb001080000
> kernel config: https://syzkaller.appspot.com/x/.config?x=4c20e006003cdecb
> dashboard link: https://syzkaller.appspot.com/bug?extid=9543479984ae9e576000
> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

#syz fix: ext4, jbd2: add an optimized bmap for the journal inode