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Subject: Re: INFO: task hung in nbd_ioctl
To:     syzbot <syzbot+24c12fa8d218ed26011a@syzkaller.appspotmail.com>,
        axboe@kernel.dk, josef@toxicpanda.com, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, nbd@other.debian.org,
        syzkaller-bugs@googlegroups.com
References: <000000000000b1b1ee0593cce78f@google.com>
From:   Mike Christie <mchristi@redhat.com>
Message-ID: <5D93C2DD.10103@redhat.com>
Date:   Tue, 1 Oct 2019 16:19:25 -0500
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Hey Josef and nbd list,

I had a question about if there are any socket family restrictions for nbd?

The bug here is that some socket familys do not support the
sock->ops->shutdown callout, and when nbd calls kernel_sock_shutdown
their callout returns -EOPNOTSUPP. That then leaves recv_work stuck in
nbd_read_stat -> sock_xmit -> sock_recvmsg. My patch added a
flush_workqueue call, so for socket familys like AF_NETLINK in this bug
we hang like we see below.

I can just remove the flush_workqueue call in that code path since it's
not needed there, but it leaves the original bug my patch was hitting
where we leave the recv_work running which can then result in leaked
resources, or possible use after free crashes and you still get the hang
if you remove the module.

It looks like we have used kernel_sock_shutdown for a while so I thought
we might never have supported sockets that did not support the callout.
Is that correct? If so then I can just add a check for this in
nbd_add_socket and fix that bug too.


On 09/30/2019 05:39 PM, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    bb2aee77 Add linux-next specific files for 20190926
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=13385ca3600000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=e60af4ac5a01e964
> dashboard link:
> https://syzkaller.appspot.com/bug?extid=24c12fa8d218ed26011a
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12abc2a3600000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11712c05600000
> 
> The bug was bisected to:
> 
> commit e9e006f5fcf2bab59149cb38a48a4817c1b538b4
> Author: Mike Christie <mchristi@redhat.com>
> Date:   Sun Aug 4 19:10:06 2019 +0000
> 
>     nbd: fix max number of supported devs
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1226f3c5600000
> final crash:    https://syzkaller.appspot.com/x/report.txt?x=1126f3c5600000
> console output: https://syzkaller.appspot.com/x/log.txt?x=1626f3c5600000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+24c12fa8d218ed26011a@syzkaller.appspotmail.com
> Fixes: e9e006f5fcf2 ("nbd: fix max number of supported devs")
> 
> INFO: task syz-executor390:8778 can't die for more than 143 seconds.
> syz-executor390 D27432  8778   8777 0x00004004
> Call Trace:
>  context_switch kernel/sched/core.c:3384 [inline]
>  __schedule+0x828/0x1c20 kernel/sched/core.c:4065
>  schedule+0xd9/0x260 kernel/sched/core.c:4132
>  schedule_timeout+0x717/0xc50 kernel/time/timer.c:1871
>  do_wait_for_common kernel/sched/completion.c:83 [inline]
>  __wait_for_common kernel/sched/completion.c:104 [inline]
>  wait_for_common kernel/sched/completion.c:115 [inline]
>  wait_for_completion+0x29c/0x440 kernel/sched/completion.c:136
>  flush_workqueue+0x40f/0x14c0 kernel/workqueue.c:2826
>  nbd_start_device_ioctl drivers/block/nbd.c:1272 [inline]
>  __nbd_ioctl drivers/block/nbd.c:1347 [inline]
>  nbd_ioctl+0xb2e/0xc44 drivers/block/nbd.c:1387
>  __blkdev_driver_ioctl block/ioctl.c:304 [inline]
>  blkdev_ioctl+0xedb/0x1c20 block/ioctl.c:606
>  block_ioctl+0xee/0x130 fs/block_dev.c:1954
>  vfs_ioctl fs/ioctl.c:47 [inline]
>  file_ioctl fs/ioctl.c:539 [inline]
>  do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:726
>  ksys_ioctl+0xab/0xd0 fs/ioctl.c:743
>  __do_sys_ioctl fs/ioctl.c:750 [inline]
>  __se_sys_ioctl fs/ioctl.c:748 [inline]
>  __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:748
>  do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x4452d9
> Code: Bad RIP value.
> RSP: 002b:00007ffde928d288 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004452d9
> RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000004
> RBP: 0000000000000000 R08: 00000000004025b0 R09: 00000000004025b0
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000402520
> R13: 00000000004025b0 R14: 0000000000000000 R15: 0000000000000000
> INFO: task syz-executor390:8778 blocked for more than 143 seconds.
>       Not tainted 5.3.0-next-20190926 #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> syz-executor390 D27432  8778   8777 0x00004004
> Call Trace:
>  context_switch kernel/sched/core.c:3384 [inline]
>  __schedule+0x828/0x1c20 kernel/sched/core.c:4065
>  schedule+0xd9/0x260 kernel/sched/core.c:4132
>  schedule_timeout+0x717/0xc50 kernel/time/timer.c:1871
>  do_wait_for_common kernel/sched/completion.c:83 [inline]
>  __wait_for_common kernel/sched/completion.c:104 [inline]
>  wait_for_common kernel/sched/completion.c:115 [inline]
>  wait_for_completion+0x29c/0x440 kernel/sched/completion.c:136
>  flush_workqueue+0x40f/0x14c0 kernel/workqueue.c:2826
>  nbd_start_device_ioctl drivers/block/nbd.c:1272 [inline]
>  __nbd_ioctl drivers/block/nbd.c:1347 [inline]
>  nbd_ioctl+0xb2e/0xc44 drivers/block/nbd.c:1387
>  __blkdev_driver_ioctl block/ioctl.c:304 [inline]
>  blkdev_ioctl+0xedb/0x1c20 block/ioctl.c:606
>  block_ioctl+0xee/0x130 fs/block_dev.c:1954
>  vfs_ioctl fs/ioctl.c:47 [inline]
>  file_ioctl fs/ioctl.c:539 [inline]
>  do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:726
>  ksys_ioctl+0xab/0xd0 fs/ioctl.c:743
>  __do_sys_ioctl fs/ioctl.c:750 [inline]
>  __se_sys_ioctl fs/ioctl.c:748 [inline]
>  __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:748
>  do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x4452d9
> Code: Bad RIP value.
> RSP: 002b:00007ffde928d288 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004452d9
> RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000004
> RBP: 0000000000000000 R08: 00000000004025b0 R09: 00000000004025b0
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000402520
> R13: 00000000004025b0 R14: 0000000000000000 R15: 0000000000000000
> 
> Showing all locks held in the system:
> 1 lock held by khungtaskd/1066:
>  #0: ffffffff88faad80 (rcu_read_lock){....}, at:
> debug_show_all_locks+0x5f/0x27e kernel/locking/lockdep.c:5337
> 2 locks held by kworker/u5:0/1525:
>  #0: ffff8880923d0d28 ((wq_completion)knbd0-recv){+.+.}, at:
> __write_once_size include/linux/compiler.h:226 [inline]
>  #0: ffff8880923d0d28 ((wq_completion)knbd0-recv){+.+.}, at:
> arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
>  #0: ffff8880923d0d28 ((wq_completion)knbd0-recv){+.+.}, at:
> atomic64_set include/asm-generic/atomic-instrumented.h:855 [inline]
>  #0: ffff8880923d0d28 ((wq_completion)knbd0-recv){+.+.}, at:
> atomic_long_set include/asm-generic/atomic-long.h:40 [inline]
>  #0: ffff8880923d0d28 ((wq_completion)knbd0-recv){+.+.}, at:
> set_work_data kernel/workqueue.c:620 [inline]
>  #0: ffff8880923d0d28 ((wq_completion)knbd0-recv){+.+.}, at:
> set_work_pool_and_clear_pending kernel/workqueue.c:647 [inline]
>  #0: ffff8880923d0d28 ((wq_completion)knbd0-recv){+.+.}, at:
> process_one_work+0x88b/0x1740 kernel/workqueue.c:2240
>  #1: ffff8880a63b7dc0 ((work_completion)(&args->work)){+.+.}, at:
> process_one_work+0x8c1/0x1740 kernel/workqueue.c:2244
> 1 lock held by rsyslogd/8659:
> 2 locks held by getty/8749:
>  #0: ffff888098c08090 (&tty->ldisc_sem){++++}, at:
> ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
>  #1: ffffc90005f112e0 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156
> 2 locks held by getty/8750:
>  #0: ffff88808f10b090 (&tty->ldisc_sem){++++}, at:
> ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
>  #1: ffffc90005f2d2e0 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156
> 2 locks held by getty/8751:
>  #0: ffff88809a6be090 (&tty->ldisc_sem){++++}, at:
> ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
>  #1: ffffc90005f192e0 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156
> 2 locks held by getty/8752:
>  #0: ffff8880a48af090 (&tty->ldisc_sem){++++}, at:
> ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
>  #1: ffffc90005f352e0 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156
> 2 locks held by getty/8753:
>  #0: ffff88808c599090 (&tty->ldisc_sem){++++}, at:
> ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
>  #1: ffffc90005f212e0 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156
> 2 locks held by getty/8754:
>  #0: ffff88808f1a8090 (&tty->ldisc_sem){++++}, at:
> ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
>  #1: ffffc90005f392e0 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156
> 2 locks held by getty/8755:
>  #0: ffff88809ab33090 (&tty->ldisc_sem){++++}, at:
> ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
>  #1: ffffc90005f012e0 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x232/0x1c10 drivers/tty/n_tty.c:2156
> 
> =============================================
> 
> NMI backtrace for cpu 1
> CPU: 1 PID: 1066 Comm: khungtaskd Not tainted 5.3.0-next-20190926 #0
> 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+0x172/0x1f0 lib/dump_stack.c:113
>  nmi_cpu_backtrace.cold+0x70/0xb2 lib/nmi_backtrace.c:101
>  nmi_trigger_cpumask_backtrace+0x23b/0x28b 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:146 [inline]
>  check_hung_uninterruptible_tasks kernel/hung_task.c:269 [inline]
>  watchdog+0xc99/0x1360 kernel/hung_task.c:353
>  kthread+0x361/0x430 kernel/kthread.c:255
>  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
> Sending NMI from CPU 1 to CPUs 0:
> NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0xe/0x10
> arch/x86/include/asm/irqflags.h:60
> 
> 
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
> 
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> For information about bisection process see:
> https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches