INFO: task hung in vfs_unlink (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 4707d8e5 Linux 4.19.126
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=113b99a6100000
kernel config: https://syzkaller.appspot.com/x/.config?x=cedcec061125e487
dashboard link: https://syzkaller.appspot.com/bug?extid=08ee2bfc429dd0f74021
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+08ee2b...@syzkaller.appspotmail.com

NOHZ: local_softirq_pending 08
NOHZ: local_softirq_pending 08
INFO: task syz-executor.0:6467 blocked for more than 140 seconds.
Not tainted 4.19.126-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.0 D23952 6467 1 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2826 [inline]
__schedule+0x8a2/0x1fc0 kernel/sched/core.c:3515
schedule+0x8d/0x1b0 kernel/sched/core.c:3559
__rwsem_down_write_failed_common kernel/locking/rwsem-xadd.c:589 [inline]
rwsem_down_write_failed+0x3d4/0x7a0 kernel/locking/rwsem-xadd.c:618
call_rwsem_down_write_failed+0x13/0x20 arch/x86/lib/rwsem.S:117
__down_write arch/x86/include/asm/rwsem.h:142 [inline]
down_write+0x4f/0x90 kernel/locking/rwsem.c:72
inode_lock include/linux/fs.h:748 [inline]
vfs_unlink+0xca/0x4e0 fs/namei.c:3993
do_unlinkat+0x3bb/0x670 fs/namei.c:4065
do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c817
Code: Bad RIP value.
RSP: 002b:00007ffc10239e28 EFLAGS: 00000246 ORIG_RAX: 0000000000000057
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000045c817
RDX: 00007ffc10239e40 RSI: 00007ffc10239e40 RDI: 00007ffc10239ed0
RBP: 0000000000002b88 R08: 0000000000000000 R09: 0000000000000019
R10: 0000000000000012 R11: 0000000000000246 R12: 00007ffc1023af60
R13: 000000000218b940 R14: 0000000000000000 R15: 00007ffc1023af60

Showing all locks held in the system:
1 lock held by khungtaskd/1079:
#0: 000000007b657168 (rcu_read_lock){....}, at: debug_show_all_locks+0x53/0x265 kernel/locking/lockdep.c:4440
1 lock held by in:imklog/6176:
#0: 00000000ff0fdfd5 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0xe3/0x100 fs/file.c:767
3 locks held by syz-executor.0/6467:
#0: 00000000496ff4f2 (sb_writers#3){.+.+}, at: sb_start_write include/linux/fs.h:1579 [inline]
#0: 00000000496ff4f2 (sb_writers#3){.+.+}, at: mnt_want_write+0x3a/0xb0 fs/namespace.c:360
#1: 0000000043475cb7 (&type->i_mutex_dir_key#3/1){+.+.}, at: inode_lock_nested include/linux/fs.h:783 [inline]
#1: 0000000043475cb7 (&type->i_mutex_dir_key#3/1){+.+.}, at: do_unlinkat+0x27d/0x670 fs/namei.c:4051
#2: 0000000064ee7229 (&sb->s_type->i_mutex_key#9){++++}, at: inode_lock include/linux/fs.h:748 [inline]
#2: 0000000064ee7229 (&sb->s_type->i_mutex_key#9){++++}, at: vfs_unlink+0xca/0x4e0 fs/namei.c:3993
2 locks held by syz-executor.0/8685:
#0: 00000000496ff4f2 (sb_writers#3){.+.+}, at: file_start_write include/linux/fs.h:2776 [inline]
#0: 00000000496ff4f2 (sb_writers#3){.+.+}, at: vfs_write+0x463/0x540 fs/read_write.c:548
#1: 0000000064ee7229 (&sb->s_type->i_mutex_key#9){++++}, at: inode_trylock include/linux/fs.h:768 [inline]
#1: 0000000064ee7229 (&sb->s_type->i_mutex_key#9){++++}, at: ext4_file_write_iter+0x21f/0xf60 fs/ext4/file.c:238

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 1079 Comm: khungtaskd Not tainted 4.19.126-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1fc/0x2fe lib/dump_stack.c:118
nmi_cpu_backtrace.cold+0x63/0xa2 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x1a6/0x1eb lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:203 [inline]
watchdog+0x962/0xe40 kernel/hung_task.c:287
kthread+0x30b/0x410 kernel/kthread.c:246
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0xe/0x10 arch/x86/include/asm/irqflags.h:60


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.