INFO: task hung in __sync_dirty_buffer

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cbfa1702 Linux 4.14.198
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=125378f3900000
kernel config: https://syzkaller.appspot.com/x/.config?x=3990958d85b55e59
dashboard link: https://syzkaller.appspot.com/bug?extid=113a4a32dcf5b9c53b61
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15166083900000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1576b46b900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+113a4a...@syzkaller.appspotmail.com

audit: type=1400 audit(1601357270.954:8): avc: denied { execmem } for pid=6396 comm="syz-executor010" scontext=system_u:system_r:kernel_t:s0 tcontext=system_u:system_r:kernel_t:s0 tclass=process permissive=1
EXT4-fs (loop0): mounted filesystem without journal. Opts: ,errors=continue
INFO: task syz-executor010:6397 blocked for more than 140 seconds.
Not tainted 4.14.198-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor010 D27160 6397 6396 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x88b/0x1de0 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
io_schedule+0xb5/0x120 kernel/sched/core.c:5036
bit_wait_io+0x12/0x90 kernel/sched/wait_bit.c:249
__wait_on_bit_lock+0xc2/0x1d0 kernel/sched/wait_bit.c:89
out_of_line_wait_on_bit_lock+0xbc/0xd0 kernel/sched/wait_bit.c:116
wait_on_bit_lock_io include/linux/wait_bit.h:213 [inline]
__lock_buffer+0x43/0x50 fs/buffer.c:72
lock_buffer include/linux/buffer_head.h:374 [inline]
__sync_dirty_buffer+0x214/0x290 fs/buffer.c:3251
__ext4_handle_dirty_metadata+0x169/0x480 fs/ext4/ext4_jbd2.c:300
ext4_convert_inline_data_nolock+0x4ce/0xb40 fs/ext4/inline.c:1246
ext4_convert_inline_data+0x2ae/0x2fc fs/ext4/inline.c:2000
ext4_fallocate+0x106/0x1d80 fs/ext4/extents.c:4968
vfs_fallocate+0x346/0x790 fs/open.c:319
SYSC_fallocate fs/open.c:342 [inline]
SyS_fallocate+0x4a/0x80 fs/open.c:336
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x445489
RSP: 002b:00007ffebbb4f898 EFLAGS: 00000246 ORIG_RAX: 000000000000011d
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000445489
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00000000006d1018 R08: 0000000000000001 R09: 0000000000000001
R10: 000000000000ffe0 R11: 0000000000000246 R12: 00000000004025f0
R13: 0000000000402680 R14: 0000000000000000 R15: 0000000000000000

Showing all locks held in the system:
1 lock held by khungtaskd/1068:
#0: (tasklist_lock){.+.+}, at: [<ffffffff814777f4>] debug_show_all_locks+0x7c/0x21a kernel/locking/lockdep.c:4548
2 locks held by syz-executor010/6397:
#0: (sb_writers#3){.+.+}, at: [<ffffffff818c80f1>] file_start_write include/linux/fs.h:2712 [inline]
#0: (sb_writers#3){.+.+}, at: [<ffffffff818c80f1>] vfs_fallocate+0x5c1/0x790 fs/open.c:318
#1: (&ei->xattr_sem){++++}, at: [<ffffffff81c0938d>] ext4_write_lock_xattr fs/ext4/xattr.h:141 [inline]
#1: (&ei->xattr_sem){++++}, at: [<ffffffff81c0938d>] ext4_convert_inline_data+0x19d/0x2fc fs/ext4/inline.c:1998

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

NMI backtrace for cpu 1
CPU: 1 PID: 1068 Comm: khungtaskd Not tainted 4.14.198-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x1b2/0x283 lib/dump_stack.c:58
nmi_cpu_backtrace.cold+0x57/0x93 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x13a/0x17f lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:140 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:195 [inline]
watchdog+0x5b9/0xb40 kernel/hung_task.c:274
kthread+0x30d/0x420 kernel/kthread.c:232
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at pc 0xffffffff8655830e


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