From: Arnd Bergmann <arnd@arndb.de>
To: linux-kernel@vger.kernel.org
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, Greg KH <gregkh@suse.de>,
Frederic Weisbecker <fweisbec@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>,
John Kacur <jkacur@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH 04/13] tty: make termios mutex nest under tty_lock
Date: Wed, 5 May 2010 18:11:22 +0200 [thread overview]
Message-ID: <201005051811.22511.arnd@arndb.de> (raw)
In-Reply-To: <1273012433-6125-5-git-send-email-arnd@arndb.de>
On Wednesday 05 May 2010, Arnd Bergmann wrote:
> Most of these are always called without the BTM held.
> Annotate them so we know in the future which places
> to look at. If we can change the code to never
> get termios_mutex while holding the BTM, this
> will solve all lock-order problems between the two.
>
> tty_set_termios_ldisc and tty_reset_termios are currently
> the only functions that always get termios_mutex while
> already holding the BTM.
>
> tty_throttle and tty_unthrottle are called from
> receive_buf which in turn is called from a lot
> of places. It needs more investigation to prove
> that we never hold the BTM while calling these
> two.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Update: I have verified that this one is not needed
at all, because we never take the BTM/BKL while holding
termios_mutex. This is very helpful and will significantly
simplify things towards the end.
With this patch removed, my patch 13 (ldisc_mutex cleanup)
can potentially be applied again, I still need to check
some corner cases with line disciplines calling
tty_driver_flush_buffer and with v253_open calling tty->ops-write
under BTM+ldisc_mutex.
If no tty driver ever takes or releases the BTM/BKL in
their flush_buffer or write functions, things should be
fine.
Arnd
next prev parent reply other threads:[~2010-05-05 16:11 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-04 22:33 [PATCH v2 00/13] BKL conversion in tty layer Arnd Bergmann
2010-05-04 22:33 ` [PATCH 01/13] tty: replace BKL with a new tty_lock Arnd Bergmann
2010-05-04 22:33 ` [PATCH 02/13] tty: make atomic_write_lock release tty_lock Arnd Bergmann
2010-05-05 10:57 ` Alan Cox
2010-05-04 22:33 ` [PATCH 03/13] tty: make tty_port->mutex nest under tty_lock Arnd Bergmann
2010-05-04 22:33 ` [PATCH 04/13] tty: make termios mutex " Arnd Bergmann
2010-05-05 16:11 ` Arnd Bergmann [this message]
2010-05-04 22:33 ` [PATCH 05/13] tty: make ldisc_mutex " Arnd Bergmann
2010-05-04 22:33 ` [PATCH 06/13] tty: never hold BTM while getting tty_mutex Arnd Bergmann
2010-05-04 22:33 ` [PATCH 07/13] tty: give up BTM in acquire_console_sem Arnd Bergmann
2010-05-04 22:33 ` [PATCH 08/13] tty: release tty lock when blocking Arnd Bergmann
2010-05-04 22:33 ` [PATCH 09/13] tty: implement BTM as mutex instead of BKL Arnd Bergmann
2010-05-04 22:33 ` [PATCH 10/13] tty: untangle locking of wait_until_sent Arnd Bergmann
2010-05-05 19:59 ` Alan Cox
2010-05-05 21:31 ` Arnd Bergmann
2010-05-05 22:51 ` Greg KH
2010-05-05 23:52 ` Alan Cox
2010-05-24 19:00 ` Pavel Machek
2010-05-24 20:27 ` Alan Cox
2010-05-04 22:33 ` [PATCH 11/13] tty: remove tty_lock_nested Arnd Bergmann
2010-05-04 22:33 ` [PATCH 12/13] tty: remove release_tty_lock/reacquire_tty_lock Arnd Bergmann
2010-05-04 22:33 ` [PATCH 13/13] tty: turn ldisc_mutex into a regular mutex Arnd Bergmann
2010-05-05 9:18 ` Arnd Bergmann
2010-05-05 10:52 ` [PATCH v2 00/13] BKL conversion in tty layer Alan Cox
2010-05-05 12:24 ` Arnd Bergmann
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