Re: [BUG] 4.11.0-rc3 xterm hung in D state on exit, wchan is tty_release_struct

[lkml@pengaru.com]

On Wed, Mar 22, 2017 at 07:08:46PM -0700, lkml@pengaru.com wrote:
> Hello list,
> 
> After approximately one day day of running 4.11.0-rc3 with 7e54d9d reverted to
> enable regular use, this happened upon destroying an xterm:
> 
> [80817.525112] BUG: unable to handle kernel paging request at 0000000000002260
> [80817.525239] IP: n_tty_receive_buf_common+0x68/0xab0
> [80817.525312] PGD 0 
> 
> [80817.525387] Oops: 0000 [#1] PREEMPT SMP
> [80817.525452] CPU: 0 PID: 9532 Comm: kworker/u4:3 Not tainted 4.11.0-rc3-00001-gc56a355 #53
> [80817.525564] Hardware name: LENOVO 7668CTO/7668CTO, BIOS 7NETC2WW (2.22 ) 03/22/2011
> [80817.525673] Workqueue: events_unbound flush_to_ldisc
> [80817.525752] task: ffff967d91d80000 task.stack: ffff9add81f40000
> [80817.525839] RIP: 0010:n_tty_receive_buf_common+0x68/0xab0
> [80817.525917] RSP: 0018:ffff9add81f43d38 EFLAGS: 00010297
> [80817.525992] RAX: 0000000000000000 RBX: ffff967d91c98c00 RCX: 0000000000000001
> [80817.526035] RDX: ffff967e73bba58d RSI: ffff967e73bba48d RDI: ffff967d91c98cc0
> [80817.526035] RBP: ffff9add81f43dd0 R08: 0000000000000001 R09: 0000000000000000
> [80817.526035] R10: 00004980cbe001e0 R11: 0000000000000000 R12: ffff967d87aacf20
> [80817.526035] R13: ffff967e73bba58d R14: 0000000000000001 R15: ffff967e74aa8008
> [80817.526035] FS:  0000000000000000(0000) GS:ffff967e7bc00000(0000) knlGS:0000000000000000
> [80817.526035] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [80817.526035] CR2: 0000000000002260 CR3: 0000000099009000 CR4: 00000000000006f0
> [80817.526035] Call Trace:
> [80817.526035]  ? update_curr+0xbb/0x1a0
> [80817.526035]  n_tty_receive_buf2+0xf/0x20
> [80817.526035]  tty_ldisc_receive_buf+0x1d/0x50
> [80817.526035]  tty_port_default_receive_buf+0x40/0x60
> [80817.526035]  flush_to_ldisc+0x94/0xa0
> [80817.526035]  process_one_work+0x13b/0x3e0
> [80817.526035]  worker_thread+0x64/0x4a0
> [80817.526035]  kthread+0x10f/0x150
> [80817.526035]  ? process_one_work+0x3e0/0x3e0
> [80817.526035]  ? __kthread_create_on_node+0x150/0x150
> [80817.526035]  ret_from_fork+0x29/0x40
> [80817.526035] Code: 85 70 ff ff ff e8 59 75 57 00 48 8d 83 00 02 00 00 c7 45 c8 00 00 00 00 48 89 45 98 48 8d 83 28 02 00 00 48 89 45 90 48 8b 45 b8 <48> 8b b0 60 22 00 00 48 8b 08 89 f0 29 c8 f6 83 10 01 00 00 08 
> [80817.526035] RIP: n_tty_receive_buf_common+0x68/0xab0 RSP: ffff9add81f43d38
> [80817.526035] CR2: 0000000000002260
> [80817.526035] ---[ end trace 640aec4765d350f2 ]---
> 
> 
> That xterm process is stuck, and I am unable to start any new xterms, switching to virtual consoles proves useless, presumably there's an important lock held.
> 
<snip>

At a casual glance of the v4.10..v4.11-rc3 changes affecting drivers/tty, the
commit c3485e looks suspicious to me, these hunks in particular:

@@ -465,16 +465,6 @@ static void flush_to_ldisc(struct work_struct *work)
 {
        struct tty_port *port = container_of(work, struct tty_port, buf.work);
        struct tty_bufhead *buf = &port->buf;
-       struct tty_struct *tty;
-       struct tty_ldisc *disc;
-
-       tty = READ_ONCE(port->itty);
-       if (tty == NULL)
-               return;
-
-       disc = tty_ldisc_ref(tty);
-       if (disc == NULL)
-               return;
 
        mutex_lock(&buf->lock);
 
@@ -504,7 +494,7 @@ static void flush_to_ldisc(struct work_struct *work)
                        continue;
                }
 
-               count = receive_buf(disc, head, count);
+               count = receive_buf(port, head, count);
                if (!count)
                        break;
                head->read += count;
@@ -512,7 +502,6 @@ static void flush_to_ldisc(struct work_struct *work)
 
        mutex_unlock(&buf->lock);
 
-       tty_ldisc_deref(disc);
 }
 
 /**

<snip>

I'm not familiar with this code at all, but port->buf is part of port, and if
the port is destroyed as part of the tty, then perhaps port->buf (and
port->buf->lock) may become invalid on us without these:

-       tty = READ_ONCE(port->itty);
-       if (tty == NULL)
-               return;
-
-       disc = tty_ldisc_ref(tty);
-       if (disc == NULL)
-               return;

Added Rob Herring, author of c3485ee to CC list.

Regards,
Vito Caputo