Message-ID: <000000000000283c37056b4a81a5@google.com>
Date:   Thu, 03 May 2018 03:17:02 -0700
From:   syzbot <syzbot+7b2866454055e43c21e5@...kaller.appspotmail.com>
To:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: INFO: task hung in __sb_start_write

Hello,

syzbot found the following crash on:

HEAD commit:    06dd3dfeea60 Merge tag 'char-misc-4.17-rc1' of  
git://git.k...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12911087800000
kernel config:  https://syzkaller.appspot.com/x/.config?x=301513bac2f9fd9
dashboard link: https://syzkaller.appspot.com/bug?extid=7b2866454055e43c21e5
compiler:       gcc (GCC) 8.0.1 20180301 (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+7b2866454055e43c21e5@...kaller.appspotmail.com

kworker/dying (22) used greatest stack depth: 8440 bytes left
INFO: task syz-executor1:4457 blocked for more than 120 seconds.
       Not tainted 4.16.0+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor1   D21448  4457   4449 0x00000000
Call Trace:
  context_switch kernel/sched/core.c:2848 [inline]
  __schedule+0x807/0x1e40 kernel/sched/core.c:3490
  schedule+0xef/0x430 kernel/sched/core.c:3549
  __rwsem_down_read_failed_common kernel/locking/rwsem-xadd.c:269 [inline]
  rwsem_down_read_failed+0x400/0x6e0 kernel/locking/rwsem-xadd.c:286
  call_rwsem_down_read_failed+0x18/0x30 arch/x86/lib/rwsem.S:94
  __down_read arch/x86/include/asm/rwsem.h:83 [inline]
  __percpu_down_read+0x15d/0x200 kernel/locking/percpu-rwsem.c:85
  percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:49 [inline]
  percpu_down_read include/linux/percpu-rwsem.h:59 [inline]
  __sb_start_write+0x2d7/0x300 fs/super.c:1340
  sb_start_write include/linux/fs.h:1548 [inline]
  mnt_want_write+0x3f/0xc0 fs/namespace.c:386
  do_unlinkat+0x2a3/0xa10 fs/namei.c:4027
  SYSC_unlink fs/namei.c:4092 [inline]
  SyS_unlink+0x26/0x30 fs/namei.c:4090
  do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x455027
RSP: 002b:00007ffe9645abc8 EFLAGS: 00000202 ORIG_RAX: 0000000000000057
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000455027
RDX: 0000000001272983 RSI: 00007ffe9645ac60 RDI: 00007ffe9645ac60
RBP: 00007ffe9645c970 R08: 0000000000000000 R09: 0000000000000010
R10: 000000000000000a R11: 0000000000000202 R12: 0000000001272940
R13: 0000000000000000 R14: 000000000000041b R15: 000000000003297e

Showing all locks held in the system:
2 locks held by khungtaskd/878:
  #0: 00000000e417309b (rcu_read_lock){....}, at:  
check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
  #0: 00000000e417309b (rcu_read_lock){....}, at: watchdog+0x1ff/0xf60  
kernel/hung_task.c:249
  #1: 00000000a42a84b8 (tasklist_lock){.+.+}, at:  
debug_show_all_locks+0xde/0x34a kernel/locking/lockdep.c:4470
2 locks held by rs:main Q:Reg/4288:
  #0: 00000000658bb541 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x1a9/0x1e0  
fs/file.c:766
  #1: 0000000052aff78e (sb_writers#4){++++}, at: file_start_write  
include/linux/fs.h:2709 [inline]
  #1: 0000000052aff78e (sb_writers#4){++++}, at: vfs_write+0x452/0x560  
fs/read_write.c:548
2 locks held by getty/4381:
  #0: 00000000990269ba (&tty->ldisc_sem){++++}, at:  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1: 000000009f1d2051 (&ldata->atomic_read_lock){+.+.}, at:  
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4382:
  #0: 00000000ecd434e6 (&tty->ldisc_sem){++++}, at:  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1: 0000000034d736c1 (&ldata->atomic_read_lock){+.+.}, at:  
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4383:
  #0: 0000000013764982 (&tty->ldisc_sem){++++}, at:  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1: 00000000202a6e1f (&ldata->atomic_read_lock){+.+.}, at:  
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4384:
  #0: 00000000ba3d2e6d (&tty->ldisc_sem){++++}, at:  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1: 00000000e3323037 (&ldata->atomic_read_lock){+.+.}, at:  
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4385:
  #0: 00000000a3add0e7 (&tty->ldisc_sem){++++}, at:  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1: 0000000081f7b524 (&ldata->atomic_read_lock){+.+.}, at:  
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4386:
  #0: 00000000a73f06ea (&tty->ldisc_sem){++++}, at:  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1: 000000002de50dc3 (&ldata->atomic_read_lock){+.+.}, at:  
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4387:
  #0: 0000000087cccc64 (&tty->ldisc_sem){++++}, at:  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1: 000000000a3822a6 (&ldata->atomic_read_lock){+.+.}, at:  
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
1 lock held by syz-executor1/4457:
  #0: 0000000052aff78e (sb_writers#4){++++}, at: sb_start_write  
include/linux/fs.h:1548 [inline]
  #0: 0000000052aff78e (sb_writers#4){++++}, at: mnt_want_write+0x3f/0xc0  
fs/namespace.c:386
1 lock held by syz-executor7/4459:
  #0: 0000000052aff78e (sb_writers#4){++++}, at: sb_start_write  
include/linux/fs.h:1548 [inline]
  #0: 0000000052aff78e (sb_writers#4){++++}, at: mnt_want_write+0x3f/0xc0  
fs/namespace.c:386
1 lock held by syz-executor5/4460:
  #0: 0000000052aff78e (sb_writers#4){++++}, at: sb_start_write  
include/linux/fs.h:1548 [inline]
  #0: 0000000052aff78e (sb_writers#4){++++}, at: mnt_want_write+0x3f/0xc0  
fs/namespace.c:386
1 lock held by syz-executor3/4462:
  #0: 0000000052aff78e (sb_writers#4){++++}, at: sb_start_write  
include/linux/fs.h:1548 [inline]
  #0: 0000000052aff78e (sb_writers#4){++++}, at: mnt_want_write+0x3f/0xc0  
fs/namespace.c:386
2 locks held by syz-executor6/14836:
  #0: 00000000f86d1ee3 (&mm->mmap_sem){++++}, at:  
__do_page_fault+0x381/0xe40 arch/x86/mm/fault.c:1328
  #1: 0000000002ee4fbd (sb_pagefaults){++++}, at: sb_start_pagefault  
include/linux/fs.h:1577 [inline]
  #1: 0000000002ee4fbd (sb_pagefaults){++++}, at:  
ext4_page_mkwrite+0x1c8/0x1420 fs/ext4/inode.c:6074
1 lock held by syz-executor0/14842:
  #0: 0000000052aff78e (sb_writers#4){++++}, at: sb_start_write  
include/linux/fs.h:1548 [inline]
  #0: 0000000052aff78e (sb_writers#4){++++}, at: mnt_want_write+0x3f/0xc0  
fs/namespace.c:386
1 lock held by syz-executor4/14843:
  #0: 0000000052aff78e (sb_writers#4){++++}, at: sb_start_write  
include/linux/fs.h:1548 [inline]
  #0: 0000000052aff78e (sb_writers#4){++++}, at: mnt_want_write+0x3f/0xc0  
fs/namespace.c:386
1 lock held by syz-executor2/14849:
  #0: 0000000052aff78e (sb_writers#4){++++}, at: sb_start_write  
include/linux/fs.h:1548 [inline]
  #0: 0000000052aff78e (sb_writers#4){++++}, at: mnt_want_write+0x3f/0xc0  
fs/namespace.c:386

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

NMI backtrace for cpu 1
CPU: 1 PID: 878 Comm: khungtaskd Not tainted 4.16.0+ #1
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+0x1b9/0x29f lib/dump_stack.c:53
  nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103
  nmi_trigger_cpumask_backtrace+0x151/0x192 lib/nmi_backtrace.c:62
  arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
  trigger_all_cpu_backtrace include/linux/nmi.h:138 [inline]
  check_hung_task kernel/hung_task.c:132 [inline]
  check_hung_uninterruptible_tasks kernel/hung_task.c:190 [inline]
  watchdog+0xc10/0xf60 kernel/hung_task.c:249
  kthread+0x345/0x410 kernel/kthread.c:238
  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:411
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0x6/0x10  
arch/x86/include/asm/irqflags.h:54


---
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