From: Ingo Molnar <mingo@elte.hu>
To: "David S. Miller" <davem@davemloft.net>
Cc: davidm@hpl.hp.com, davidm@napali.hpl.hp.com, tony.luck@intel.com,
linux-kernel@vger.kernel.org
Subject: Re: [patch] sched: unlocked context-switches
Date: Sun, 10 Apr 2005 08:43:24 +0200 [thread overview]
Message-ID: <20050410064324.GA24596@elte.hu> (raw)
In-Reply-To: <20050409155810.593d8f7b.davem@davemloft.net>
* David S. Miller <davem@davemloft.net> wrote:
> > Yes, of course. The deadlock was due to context-switching, not
> > switch_mm() per se. Hopefully someone else beats me to remembering
> > the details before Monday.
>
> Sparc64 has a deadlock because we hold mm->page_table_lock during
> switch_mm(). I bet IA64 did something similar, as I remember it had a
> very similar locking issue in this area.
>
> So the deadlock was, we held the runqueue locks over switch_mm(),
> switch_mm() spins on mm->page_table_lock, the cpu which does have
> mm->page_table_lock tries to do a wakeup on the first cpu's runqueue.
> Classic AB-BA deadlock.
yeah, i can see that happening - holding the runqueue lock and enabling
interrupts. (it's basically never safe to enable irqs with the runqueue
lock held.)
the patch drops both the runqueue lock and enables interrupts, so this
particular issue should not trigger.
Ingo
next prev parent reply other threads:[~2005-04-10 6:43 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <3R6Ir-89Y-23@gated-at.bofh.it>
2005-04-09 6:32 ` [patch] sched: unlocked context-switches David Mosberger-Tang
2005-04-09 7:07 ` Ingo Molnar
2005-04-09 7:15 ` David Mosberger
2005-04-09 22:58 ` David S. Miller
2005-04-10 6:43 ` Ingo Molnar [this message]
2005-04-12 1:06 ` David Mosberger
2005-04-12 2:12 ` Nick Piggin
2005-04-12 17:14 ` David Mosberger
2005-04-13 3:26 ` Nick Piggin
2005-04-12 6:42 ` Ingo Molnar
2005-04-12 17:15 ` David Mosberger
2005-04-08 18:38 Luck, Tony
2005-04-09 4:38 ` Ingo Molnar
2005-04-09 6:28 ` Nick Piggin
2005-04-09 6:55 ` Ingo Molnar
2005-04-09 7:11 ` Nick Piggin
2005-04-09 9:22 ` Benjamin Herrenschmidt
2005-04-09 22:46 ` David S. Miller
2005-04-10 7:23 ` Richard Henderson
-- strict thread matches above, loose matches on Subject: below --
2005-04-08 12:16 Ingo Molnar
2005-04-29 9:09 ` Andrew Morton
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