INFO: task hung in rmap_walk_file

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 815e34f8 Merge 4.14.90 into android-4.14
git tree: android-4.14
console output: https://syzkaller.appspot.com/x/log.txt?x=154348c3400000
kernel config: https://syzkaller.appspot.com/x/.config?x=608dc5a2664d6079
dashboard link: https://syzkaller.appspot.com/bug?extid=0fb896af0d131221e0d7
compiler: gcc (GCC) 8.0.1 20180413 (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+0fb896...@syzkaller.appspotmail.com

INFO: task syz-executor4:2368 blocked for more than 140 seconds.
Not tainted 4.14.90+ #29
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor4 D26808 2368 1848 0x80000000
Call Trace:
schedule+0x7f/0x1b0 kernel/sched/core.c:3490
__rwsem_down_read_failed_common kernel/locking/rwsem-xadd.c:269 [inline]
rwsem_down_read_failed+0x21a/0x3d0 kernel/locking/rwsem-xadd.c:286
call_rwsem_down_read_failed+0x14/0x30 arch/x86/lib/rwsem.S:94
__down_read arch/x86/include/asm/rwsem.h:66 [inline]
down_read+0x45/0xa0 kernel/locking/rwsem.c:26
i_mmap_lock_read include/linux/fs.h:480 [inline]
rmap_walk_file+0x38d/0x4f0 mm/rmap.c:1819
rmap_walk+0xe5/0x170 mm/rmap.c:1847
try_to_munlock+0x178/0x260 mm/rmap.c:1698
__munlock_isolated_page+0xbf/0x220 mm/mlock.c:132
__munlock_pagevec+0x4c9/0x9b0 mm/mlock.c:340
munlock_vma_pages_range+0x4c7/0x580 mm/mlock.c:493
munlock_vma_pages_all mm/internal.h:293 [inline]
exit_mmap+0x183/0x420 mm/mmap.c:3052
__mmput kernel/fork.c:929 [inline]
mmput+0xc8/0x350 kernel/fork.c:950
exit_mm kernel/exit.c:544 [inline]
do_exit+0x843/0x28c0 kernel/exit.c:852
do_group_exit+0x100/0x2e0 kernel/exit.c:968
get_signal+0x4e5/0x1470 kernel/signal.c:2348
do_signal+0x8f/0x1660 arch/x86/kernel/signal.c:809
exit_to_usermode_loop+0x116/0x150 arch/x86/entry/common.c:159
prepare_exit_to_usermode arch/x86/entry/common.c:198 [inline]
syscall_return_slowpath arch/x86/entry/common.c:267 [inline]
do_syscall_64+0x35d/0x4b0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x457669
RSP: 002b:00007f8362e86cf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 000000000072c048 RCX: 0000000000457669
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 000000000072c048
RBP: 000000000072c040 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000072c04c
R13: 00007ffd2b3da80f R14: 00007f8362e879c0 R15: 000000000072c04c

Showing all locks held in the system:
1 lock held by khungtaskd/23:
#0: (tasklist_lock){.+.+}, at: [<ffffffffac004837>]
debug_show_all_locks+0x74/0x20f kernel/locking/lockdep.c:4541
2 locks held by getty/1758:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffffacb40c20>]
tty_ldisc_ref_wait+0x20/0x80 drivers/tty/tty_ldisc.c:275
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffffacb3c07f>]
n_tty_read+0x1ff/0x1700 drivers/tty/n_tty.c:2156
1 lock held by syz-executor4/2368:
#0: (&mapping->i_mmap_rwsem){++++}, at: [<ffffffffac2f299d>]
i_mmap_lock_read include/linux/fs.h:480 [inline]
#0: (&mapping->i_mmap_rwsem){++++}, at: [<ffffffffac2f299d>]
rmap_walk_file+0x38d/0x4f0 mm/rmap.c:1819

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

NMI backtrace for cpu 0
CPU: 0 PID: 23 Comm: khungtaskd Not tainted 4.14.90+ #29
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0xb9/0x11b lib/dump_stack.c:53
nmi_cpu_backtrace.cold.0+0x47/0x85 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x121/0x146 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:140 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:196 [inline]
watchdog+0x574/0xa70 kernel/hung_task.c:252
kthread+0x348/0x420 kernel/kthread.c:232
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:402
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at pc 0xffffffffad66a722


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[syzbot]

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