Re: [syzbot] INFO: task hung in vhost_work_dev_flush
From: Anirudh Rayabharam
Date: Mon Feb 21 2022 - 10:53:28 EST
On Mon, Feb 21, 2022 at 03:12:33PM +0100, Stefano Garzarella wrote:
> #syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
> f71077a4d84b
>
> Patch sent upstream:
> https://lore.kernel.org/virtualization/20220221114916.107045-1-sgarzare@xxxxxxxxxx/T/#u
I don't see how your patch fixes this issue. It looks unrelated. It is
surprising that syzbot is happy with it.
I have sent a patch for this issue here:
https://lore.kernel.org/lkml/20220221072852.31820-1-mail@xxxxxxxxxxxxx/
Thanks!
- Anirudh
>
> On Sat, Feb 19, 2022 at 12:23 AM syzbot
> <syzbot+0abd373e2e50d704db87@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit: e6251ab4551f Merge tag 'nfs-for-5.17-2' of git://git.linux..
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=163caa3c700000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=266de9da75c71a45
> > dashboard link: https://syzkaller.appspot.com/bug?extid=0abd373e2e50d704db87
> > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=108514a4700000
> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16ca671c700000
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+0abd373e2e50d704db87@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > INFO: task syz-executor117:3632 blocked for more than 143 seconds.
> > Not tainted 5.17.0-rc3-syzkaller-00029-ge6251ab4551f #0
> > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > task:syz-executor117 state:D stack:27512 pid: 3632 ppid: 3631 flags:0x00004002
> > Call Trace:
> > <TASK>
> > context_switch kernel/sched/core.c:4986 [inline]
> > __schedule+0xab2/0x4db0 kernel/sched/core.c:6295
> > schedule+0xd2/0x260 kernel/sched/core.c:6368
> > schedule_timeout+0x1db/0x2a0 kernel/time/timer.c:1857
> > do_wait_for_common kernel/sched/completion.c:85 [inline]
> > __wait_for_common kernel/sched/completion.c:106 [inline]
> > wait_for_common kernel/sched/completion.c:117 [inline]
> > wait_for_completion+0x174/0x270 kernel/sched/completion.c:138
> > vhost_work_dev_flush.part.0+0xbb/0xf0 drivers/vhost/vhost.c:243
> > vhost_work_dev_flush drivers/vhost/vhost.c:238 [inline]
> > vhost_poll_flush+0x5e/0x80 drivers/vhost/vhost.c:252
> > vhost_vsock_flush drivers/vhost/vsock.c:710 [inline]
> > vhost_vsock_dev_release+0x1be/0x4b0 drivers/vhost/vsock.c:757
> > __fput+0x286/0x9f0 fs/file_table.c:311
> > task_work_run+0xdd/0x1a0 kernel/task_work.c:164
> > exit_task_work include/linux/task_work.h:32 [inline]
> > do_exit+0xb29/0x2a30 kernel/exit.c:806
> > do_group_exit+0xd2/0x2f0 kernel/exit.c:935
> > __do_sys_exit_group kernel/exit.c:946 [inline]
> > __se_sys_exit_group kernel/exit.c:944 [inline]
> > __x64_sys_exit_group+0x3a/0x50 kernel/exit.c:944
> > do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> > entry_SYSCALL_64_after_hwframe+0x44/0xae
> > RIP: 0033:0x7fbf04b83b89
> > RSP: 002b:00007fff5bc9ca18 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> > RAX: ffffffffffffffda RBX: 00007fbf04bf8330 RCX: 00007fbf04b83b89
> > RDX: 000000000000003c RSI: 00000000000000e7 RDI: 0000000000000000
> > RBP: 0000000000000000 R08: ffffffffffffffc0 R09: 00007fff5bc9cc08
> > R10: 00007fff5bc9cc08 R11: 0000000000000246 R12: 00007fbf04bf8330
> > R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000001
> > </TASK>
> >
> > Showing all locks held in the system:
> > 1 lock held by khungtaskd/26:
> > #0: ffffffff8bb83c20 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:6460
> > 2 locks held by getty/3275:
> > #0: ffff88807f0db098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:244
> > #1: ffffc90002b662e8 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0xcf0/0x1230 drivers/tty/n_tty.c:2077
> > 1 lock held by vhost-3632/3633:
> >
> > =============================================
> >
> > NMI backtrace for cpu 0
> > CPU: 0 PID: 26 Comm: khungtaskd Not tainted 5.17.0-rc3-syzkaller-00029-ge6251ab4551f #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > Call Trace:
> > <TASK>
> > __dump_stack lib/dump_stack.c:88 [inline]
> > dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
> > nmi_cpu_backtrace.cold+0x47/0x144 lib/nmi_backtrace.c:111
> > nmi_trigger_cpumask_backtrace+0x1b3/0x230 lib/nmi_backtrace.c:62
> > trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
> > check_hung_uninterruptible_tasks kernel/hung_task.c:212 [inline]
> > watchdog+0xc1d/0xf50 kernel/hung_task.c:369
> > kthread+0x2e9/0x3a0 kernel/kthread.c:377
> > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
> > </TASK>
> > Sending NMI from CPU 0 to CPUs 1:
> > NMI backtrace for cpu 1
> > CPU: 1 PID: 3633 Comm: vhost-3632 Not tainted 5.17.0-rc3-syzkaller-00029-ge6251ab4551f #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > RIP: 0010:check_kcov_mode kernel/kcov.c:166 [inline]
> > RIP: 0010:__sanitizer_cov_trace_pc+0xd/0x60 kernel/kcov.c:200
> > Code: 00 00 e9 c6 41 66 02 66 0f 1f 44 00 00 48 8b be b0 01 00 00 e8 b4 ff ff ff 31 c0 c3 90 65 8b 05 29 f7 89 7e 89 c1 48 8b 34 24 <81> e1 00 01 00 00 65 48 8b 14 25 00 70 02 00 a9 00 01 ff 00 74 0e
> > RSP: 0018:ffffc90000cd7c78 EFLAGS: 00000246
> > RAX: 0000000080000000 RBX: ffff888079ca8a80 RCX: 0000000080000000
> > RDX: 0000000000000000 RSI: ffffffff86d3f8fb RDI: 0000000000000003
> > RBP: 0000000000000000 R08: 0000000000000000 R09: ffffc90000cd7c77
> > R10: ffffffff86d3f8ed R11: 0000000000000001 R12: 0000000000000000
> > R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000000
> > FS: 0000000000000000(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00007ffdf716a3b8 CR3: 00000000235b6000 CR4: 00000000003506e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> > <TASK>
> > iotlb_access_ok+0x21b/0x3e0 drivers/vhost/vhost.c:1340
> > vq_meta_prefetch+0xbc/0x280 drivers/vhost/vhost.c:1366
> > vhost_transport_do_send_pkt+0xe0/0xfd0 drivers/vhost/vsock.c:104
> > vhost_worker+0x23d/0x3d0 drivers/vhost/vhost.c:372
> > kthread+0x2e9/0x3a0 kernel/kthread.c:377
> > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
> > </TASK>
> > ----------------
> > Code disassembly (best guess):
> > 0: 00 00 add %al,(%rax)
> > 2: e9 c6 41 66 02 jmpq 0x26641cd
> > 7: 66 0f 1f 44 00 00 nopw 0x0(%rax,%rax,1)
> > d: 48 8b be b0 01 00 00 mov 0x1b0(%rsi),%rdi
> > 14: e8 b4 ff ff ff callq 0xffffffcd
> > 19: 31 c0 xor %eax,%eax
> > 1b: c3 retq
> > 1c: 90 nop
> > 1d: 65 8b 05 29 f7 89 7e mov %gs:0x7e89f729(%rip),%eax # 0x7e89f74d
> > 24: 89 c1 mov %eax,%ecx
> > 26: 48 8b 34 24 mov (%rsp),%rsi
> > * 2a: 81 e1 00 01 00 00 and $0x100,%ecx <-- trapping instruction
> > 30: 65 48 8b 14 25 00 70 mov %gs:0x27000,%rdx
> > 37: 02 00
> > 39: a9 00 01 ff 00 test $0xff0100,%eax
> > 3e: 74 0e je 0x4e
> >
> >
> > ---
> > This report 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@xxxxxxxxxxxxxxxx.
> >
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > syzbot can test patches for this issue, for details see:
> > https://goo.gl/tpsmEJ#testing-patches
> >
>
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> From 4951112bf98d3e10d3e9557986e5ca5419ca738f Mon Sep 17 00:00:00 2001
> From: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> Date: Mon, 21 Feb 2022 11:07:49 +0100
> Subject: [PATCH] vhost/vsock: don't check owner in vhost_vsock_stop() while
> releasing
>
> vhost_vsock_stop() calls vhost_dev_check_owner() to check the device
> ownership. It expects current->mm to be valid.
>
> vhost_vsock_stop() is also called by vhost_vsock_dev_release() when
> the user has not done close(), so when we are in do_exit(). In this
> case current->mm is invalid and we're releasing the device, so we
> should clean it anyway.
>
> Let's check the owner only when vhost_vsock_stop() is called
> by an ioctl.
>
> Fixes: 433fc58e6bf2 ("VSOCK: Introduce vhost_vsock.ko")
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: syzbot+1e3ea63db39f2b4440e0@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> ---
> drivers/vhost/vsock.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index d6ca1c7ad513..f00d2dfd72b7 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -629,16 +629,18 @@ static int vhost_vsock_start(struct vhost_vsock *vsock)
> return ret;
> }
>
> -static int vhost_vsock_stop(struct vhost_vsock *vsock)
> +static int vhost_vsock_stop(struct vhost_vsock *vsock, bool check_owner)
> {
> size_t i;
> int ret;
>
> mutex_lock(&vsock->dev.mutex);
>
> - ret = vhost_dev_check_owner(&vsock->dev);
> - if (ret)
> - goto err;
> + if (check_owner) {
> + ret = vhost_dev_check_owner(&vsock->dev);
> + if (ret)
> + goto err;
> + }
>
> for (i = 0; i < ARRAY_SIZE(vsock->vqs); i++) {
> struct vhost_virtqueue *vq = &vsock->vqs[i];
> @@ -753,7 +755,7 @@ static int vhost_vsock_dev_release(struct inode *inode, struct file *file)
> * inefficient. Room for improvement here. */
> vsock_for_each_connected_socket(vhost_vsock_reset_orphans);
>
> - vhost_vsock_stop(vsock);
> + vhost_vsock_stop(vsock, false);
> vhost_vsock_flush(vsock);
> vhost_dev_stop(&vsock->dev);
>
> @@ -868,7 +870,7 @@ static long vhost_vsock_dev_ioctl(struct file *f, unsigned int ioctl,
> if (start)
> return vhost_vsock_start(vsock);
> else
> - return vhost_vsock_stop(vsock);
> + return vhost_vsock_stop(vsock, true);
> case VHOST_GET_FEATURES:
> features = VHOST_VSOCK_FEATURES;
> if (copy_to_user(argp, &features, sizeof(features)))
> --
> 2.35.1
>