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Date:   Thu, 17 Oct 2019 15:03:30 +0100
From:   "Richard W.M. Jones" <rjones@redhat.com>
To:     Mike Christie <mchristi@redhat.com>
Cc:     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
Subject: Re: INFO: task hung in nbd_ioctl
Message-ID: <20191017140330.GB25667@redhat.com>
References: <000000000000b1b1ee0593cce78f@google.com>
 <5D93C2DD.10103@redhat.com>
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On Tue, Oct 01, 2019 at 04:19:25PM -0500, Mike Christie wrote:
> Hey Josef and nbd list,
> 
> I had a question about if there are any socket family restrictions for nbd?

In normal circumstances, in userspace, the NBD protocol would only be
used over AF_UNIX or AF_INET/AF_INET6.

There's a bit of confusion because netlink is used by nbd-client to
configure the NBD device, setting things like block size and timeouts
(instead of ioctl which is deprecated).  I think you don't mean this
use of netlink?

> 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.

Rich.

> 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

-- 
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