From: Alan Cox <alan@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ming Lei <ming.lei@canonical.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH] tty: tty_mutex: fix lockdep warning in tty_lock_pair(v1)
Date: Fri, 25 May 2012 14:47:13 +0100 [thread overview]
Message-ID: <20120525144713.6946df1e@bob.linux.org.uk> (raw)
In-Reply-To: <1337952533.9783.195.camel@laptop>
> Having looked at the source I still don't see how it could possibly
> work,.. So the problem with tty_release() -> tty_ldisc_release() is
> that tty_ldisc_release() does an unlock/lock of tty.
Yes it should do the pair, see the patch I posted restructing it, and
the second one restructing it right.
> However your tty_lock_pair() can still result in tty being subclass 1,
> see your else branch, nested case.
>
> That said, how is this not a real deadlock? If you rely on tty pointer
> ordering to avoid deadlocks, you always need to lock them in the same
> order. The unlock+lock in ldisc_release violates that.
Which was a bug.
Alan
next prev parent reply other threads:[~2012-05-25 13:31 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-22 1:58 [PATCH] tty: tty_mutex: fix lockdep warning in tty_lock_pair(v1) Ming Lei
2012-05-23 6:01 ` Ming Lei
2012-05-25 13:28 ` Peter Zijlstra
2012-05-25 13:39 ` Peter Zijlstra
2012-05-25 13:47 ` Alan Cox [this message]
2012-05-25 13:52 ` Peter Zijlstra
2012-05-25 14:01 ` Alan Cox
2012-05-25 14:08 ` Peter Zijlstra
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