From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Dmitry Safonov <dima@arista.com>
Cc: linux-kernel@vger.kernel.org,
"Dmitry Safonov" <0x7f454c46@gmail.com>,
"Daniel Axtens" <dja@axtens.net>,
"Dmitry Vyukov" <dvyukov@google.com>,
"Mark Rutland" <mark.rutland@arm.com>,
"Michael Neuling" <mikey@neuling.org>,
"Mikulas Patocka" <mpatocka@redhat.com>,
"Nathan March" <nathan@gt.net>, "Pasi Kärkkäinen" <pasik@iki.fi>,
"Peter Hurley" <peter@hurleysoftware.com>,
"Peter Zijlstra" <peterz@infradead.org>,
"Rong, Chen" <rong.a.chen@intel.com>,
"Sergey Senozhatsky" <sergey.senozhatsky.work@gmail.com>,
"Tan Xiaojun" <tanxiaojun@huawei.com>,
"Tetsuo Handa" <penguin-kernel@I-love.SAKURA.ne.jp>,
"Jiri Slaby" <jslaby@suse.com>
Subject: Re: [PATCHv5 2/7] tty/ldsem: Wake up readers after timed out down_write()
Date: Tue, 18 Sep 2018 15:43:47 +0200 [thread overview]
Message-ID: <20180918134347.GD23431@kroah.com> (raw)
In-Reply-To: <20180917235258.5719-3-dima@arista.com>
On Tue, Sep 18, 2018 at 12:52:53AM +0100, Dmitry Safonov wrote:
> ldsem_down_read() will sleep if there is pending writer in the queue.
> If the writer times out, readers in the queue should be woken up,
> otherwise they may miss a chance to acquire the semaphore until the last
> active reader will do ldsem_up_read().
>
> There was a couple of reports where there was one active reader and
> other readers soft locked up:
> Showing all locks held in the system:
> 2 locks held by khungtaskd/17:
> #0: (rcu_read_lock){......}, at: watchdog+0x124/0x6d1
> #1: (tasklist_lock){.+.+..}, at: debug_show_all_locks+0x72/0x2d3
> 2 locks held by askfirst/123:
> #0: (&tty->ldisc_sem){.+.+.+}, at: ldsem_down_read+0x46/0x58
> #1: (&ldata->atomic_read_lock){+.+...}, at: n_tty_read+0x115/0xbe4
>
> Prevent readers wait for active readers to release ldisc semaphore.
>
> Link: lkml.kernel.org/r/<20171121132855.ajdv4k6swzhvktl6@wfg-t540p.sh.intel.com>
> Link: lkml.kernel.org/r/<20180907045041.GF1110@shao2-debian>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Jiri Slaby <jslaby@suse.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Reported-by: kernel test robot <rong.a.chen@intel.com>
> Signed-off-by: Dmitry Safonov <dima@arista.com>
> ---
Why isn't this ok for the stable trees?
thanks,
greg k-h
next prev parent reply other threads:[~2018-09-18 13:45 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-17 23:52 [PATCHv5 0/7] tty: Hold write ldisc sem in tty_reopen() Dmitry Safonov
2018-09-17 23:52 ` [PATCHv5 1/7] tty: Drop tty->count on tty_reopen() failure Dmitry Safonov
2018-09-18 13:41 ` Greg Kroah-Hartman
2018-09-18 14:15 ` Dmitry Safonov
2018-09-17 23:52 ` [PATCHv5 2/7] tty/ldsem: Wake up readers after timed out down_write() Dmitry Safonov
2018-09-18 13:43 ` Greg Kroah-Hartman [this message]
2018-09-18 14:12 ` Dmitry Safonov
2018-09-17 23:52 ` [PATCHv5 3/7] tty: Hold tty_ldisc_lock() during tty_reopen() Dmitry Safonov
2018-09-18 13:47 ` Greg Kroah-Hartman
2018-09-18 14:19 ` Dmitry Safonov
2018-09-17 23:52 ` [PATCHv5 4/7] tty: Simplify tty->count math in tty_reopen() Dmitry Safonov
2018-09-17 23:52 ` [PATCHv5 5/7] tty/ldsem: Convert to regular lockdep annotations Dmitry Safonov
2018-09-17 23:52 ` [PATCHv5 6/7] tty/ldsem: Add lockdep asserts for ldisc_sem Dmitry Safonov
2018-09-18 13:49 ` Greg Kroah-Hartman
2018-09-18 14:21 ` Dmitry Safonov
2018-09-17 23:52 ` [PATCHv5 7/7] tty/ldsem: Decrement wait_readers on timeouted down_read() Dmitry Safonov
2018-09-19 16:56 ` [PATCHv5 0/7] tty: Hold write ldisc sem in tty_reopen() Mikulas Patocka
2018-09-19 17:35 ` Mikulas Patocka
2018-09-19 17:45 ` Dmitry Safonov
2018-09-19 20:03 ` Mikulas Patocka
2018-09-19 20:21 ` Dmitry Safonov
2018-09-20 14:25 ` Mikulas Patocka
2018-10-15 13:37 ` Pasi Kärkkäinen
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