Subject: INFO: task hung in p9_fd_close

From: syzbot <[email-masked]>
Date: Fri, 30 Aug 2019 12:28:07 -0700

Hello,

syzbot found the following crash on:

HEAD commit:    6525771f Merge tag 'arc-5.3-rc7' of git://git.kernel.org/p..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1118a71e600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=58485246ad14eafe
dashboard link: https://syzkaller.appspot.com/bug?extid=8b41a1365f1106fd0f33
compiler:       clang version 9.0.0 (/home/glider/llvm/clang  
80fee25776c2fb61e74c1ecb1a523375c2500b69)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1125ee12600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email-masked]

INFO: task syz-executor.1:13699 blocked for more than 143 seconds.
       Not tainted 5.3.0-rc6+ #94
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.1  D28888 13699   9148 0x00004004
Call Trace:
  context_switch kernel/sched/core.c:3254 [inline]
  __schedule+0x877/0xc50 kernel/sched/core.c:3880
  schedule+0x131/0x1e0 kernel/sched/core.c:3947
  schedule_timeout+0x46/0x240 kernel/time/timer.c:1783
  do_wait_for_common+0x2e7/0x4d0 kernel/sched/completion.c:83
  __wait_for_common kernel/sched/completion.c:104 [inline]
  wait_for_common kernel/sched/completion.c:115 [inline]
  wait_for_completion+0x47/0x60 kernel/sched/completion.c:136
  __flush_work+0xd4/0x150 kernel/workqueue.c:3040
  __cancel_work_timer+0x420/0x570 kernel/workqueue.c:3127
  cancel_work_sync+0x17/0x20 kernel/workqueue.c:3163
  p9_conn_destroy net/9p/trans_fd.c:868 [inline]
  p9_fd_close+0x297/0x3c0 net/9p/trans_fd.c:898
  p9_client_create+0x974/0xee0 net/9p/client.c:1068
  v9fs_session_init+0x192/0x18e0 fs/9p/v9fs.c:406
  v9fs_mount+0x82/0x810 fs/9p/vfs_super.c:120
  legacy_get_tree+0xf9/0x1a0 fs/fs_context.c:661
  vfs_get_tree+0x8f/0x380 fs/super.c:1413
  do_new_mount fs/namespace.c:2791 [inline]
  do_mount+0x169d/0x2490 fs/namespace.c:3111
  ksys_mount+0xcc/0x100 fs/namespace.c:3320
  __do_sys_mount fs/namespace.c:3334 [inline]
  __se_sys_mount fs/namespace.c:3331 [inline]
  __x64_sys_mount+0xbf/0xd0 fs/namespace.c:3331
  do_syscall_64+0xfe/0x140 arch/x86/entry/common.c:296
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459879
Code: 8b 44 24 18 48 8b 4c 24 30 48 83 c1 08 48 89 0c 24 48 89 44 24 08 48  
c7 44 24 10 10 00 00 00 e8 0d da fa ff 48 8b 44 24 18 48 <89> 44 24 40 48  
8b 6c 24 20 48 83 c4 28 c3 e8 14 b9 ff ff eb 82 cc
RSP: 002b:00007f6b4dda7c78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000459879
RDX: 0000000020000140 RSI: 0000000020000000 RDI: 0000000000000000
RBP: 000000000075c118 R08: 0000000020000480 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f6b4dda86d4
R13: 00000000004c5e2f R14: 00000000004da930 R15: 00000000ffffffff
INFO: lockdep is turned off.
NMI backtrace for cpu 0
CPU: 0 PID: 1057 Comm: khungtaskd Not tainted 5.3.0-rc6+ #94
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+0x1d8/0x2f8 lib/dump_stack.c:113
  nmi_cpu_backtrace+0xaf/0x1a0 lib/nmi_backtrace.c:101
  nmi_trigger_cpumask_backtrace+0x174/0x290 lib/nmi_backtrace.c:62
  arch_trigger_cpumask_backtrace+0x10/0x20 arch/x86/kernel/apic/hw_nmi.c:38
  trigger_all_cpu_backtrace+0x17/0x20 include/linux/nmi.h:146
  check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
  watchdog+0xbb9/0xbd0 kernel/hung_task.c:289
  kthread+0x332/0x350 kernel/kthread.c:255
  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at native_safe_halt+0xe/0x10  
arch/x86/include/asm/irqflags.h:60

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