linux-kernel - Re: [linux-next / tty] possible circular locking dependency detected

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Date:   Mon, 22 May 2017 12:26:46 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [linux-next / tty] possible circular locking dependency detected

On 05/22/2017, 12:24 PM, Greg Kroah-Hartman wrote:
> On Mon, May 22, 2017 at 04:39:43PM +0900, Sergey Senozhatsky wrote:
>> Hello,
>>
>> [ 1274.378287] ======================================================
>> [ 1274.378289] WARNING: possible circular locking dependency detected
>> [ 1274.378290] 4.12.0-rc1-next-20170522-dbg-00007-gc09b2ab28b74-dirty #1317 Not tainted
>> [ 1274.378291] ------------------------------------------------------
>> [ 1274.378293] kworker/u8:5/111 is trying to acquire lock:
>> [ 1274.378294]  (&buf->lock){+.+...}, at: [<ffffffff812f2831>] tty_buffer_flush+0x34/0x88
>> [ 1274.378300] 
>>                but task is already holding lock:
>> [ 1274.378301]  (&o_tty->termios_rwsem/1){++++..}, at: [<ffffffff812ee5c7>] isig+0x47/0xd2
>> [ 1274.378307] 
>>                which lock already depends on the new lock.
>>
>> [ 1274.378309] 
>>                the existing dependency chain (in reverse order) is:
>> [ 1274.378310] 
>>                -> #2 (&o_tty->termios_rwsem/1){++++..}:
>> [ 1274.378316]        lock_acquire+0x183/0x1ae
>> [ 1274.378319]        down_read+0x3e/0x62
>> [ 1274.378321]        n_tty_write+0x6c/0x3d6
>> [ 1274.378322]        tty_write+0x1cc/0x25f
>> [ 1274.378325]        __vfs_write+0x26/0xec
>> [ 1274.378327]        vfs_write+0xe1/0x16a
>> [ 1274.378329]        SyS_write+0x51/0x8e
>> [ 1274.378330]        entry_SYSCALL_64_fastpath+0x18/0xad
>> [ 1274.378331] 
>>                -> #1 (&tty->atomic_write_lock){+.+.+.}:
>> [ 1274.378335]        lock_acquire+0x183/0x1ae
>> [ 1274.378337]        __mutex_lock+0x95/0x7ba
>> [ 1274.378339]        mutex_lock_nested+0x1b/0x1d
>> [ 1274.378340]        tty_port_default_receive_buf+0x4e/0x81

...
> Does this also show up in 4.11?

According to traces, I very believe this is caused by
commit 925bb1ce47f429f69aad35876df7ecd8c53deb7e
Author: Vegard Nossum <vegard.nossum@...cle.com>
Date:   Thu May 11 12:18:52 2017 +0200

    tty: fix port buffer locking

thanks,
-- 
js
suse labs