INFO: task hung in __fdget_pos

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 63d1657d ANDROID: sched/rt: fix the problem that rt_rq's u..
git tree: android-4.14
console output: https://syzkaller.appspot.com/x/log.txt?x=17e551f8c00000
kernel config: https://syzkaller.appspot.com/x/.config?x=a8a239ffba5f9eef
dashboard link: https://syzkaller.appspot.com/bug?extid=20a01b44b276a49fff7e
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+20a01b...@syzkaller.appspotmail.com

INFO: task syz-executor0:10958 blocked for more than 140 seconds.
Not tainted 4.14.96+ #20
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0 D28024 10958 5605 0x00000004
Call Trace:
schedule+0x92/0x1c0 kernel/sched/core.c:3490
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3548
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x559/0x1430 kernel/locking/mutex.c:893
__fdget_pos+0xa6/0xc0 fs/file.c:768
fdget_pos include/linux/file.h:67 [inline]
SYSC_write fs/read_write.c:588 [inline]
SyS_write+0x72/0x1a0 fs/read_write.c:585
do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289

Showing all locks held in the system:
1 lock held by khungtaskd/23:
#0: (tasklist_lock){.+.+}, at: [<ffffffffa8dffeec>]
debug_show_all_locks+0x7c/0x21a kernel/locking/lockdep.c:4541
2 locks held by getty/1757:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffffa9936f02>]
tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:275
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffffa9932327>]
n_tty_read+0x1f7/0x1700 drivers/tty/n_tty.c:2156
1 lock held by syz-executor0/10958:
#0: (&f->f_pos_lock){+.+.}, at: [<ffffffffa91b9966>]
__fdget_pos+0xa6/0xc0 fs/file.c:768

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

NMI backtrace for cpu 1
CPU: 1 PID: 23 Comm: khungtaskd Not tainted 4.14.96+ #20
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0xb9/0x10e lib/dump_stack.c:53
nmi_cpu_backtrace.cold+0x47/0x86 lib/nmi_backtrace.c:101
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at pc 0xffffffffaa450692


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[syzbot]

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