linux-kernel - Re: kernel BUG at drivers/md/raid5.c:693!

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Message-ID: <20131126153106.6ae734c0@notabene.brown>
Date:	Tue, 26 Nov 2013 15:31:06 +1100
From:	NeilBrown <neilb@...e.de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	fengguang.wu@...el.com, "Li, Shaohua" <shaohua.li@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: kernel BUG at drivers/md/raid5.c:693!

On Mon, 25 Nov 2013 10:53:23 +0100 Peter Zijlstra <peterz@...radead.org>
wrote:

> On Mon, Nov 25, 2013 at 10:35:22AM +1100, NeilBrown wrote:
> > Ingo/Peter: is it considered OK to call wake_up while holding a spinlock?
> 
> Yes, very much so. Doing a wakeup isn't _that_ expensive.

Oh good.  Thanks.

> 
> > Could "sleeping spinlocks" affect this at all? (some sample stack traces are
> > below).
> 
> Not entirely sure, are you referencing to -rt where me make spinlock_t
> pi-mutexes?

I'm not sure either.  Just stabbing in the dark really.

The stack trace in the previous email seemed to suggest that a process was
blocking inside a wake_up call, but it wasn't at all conclusive.  And I've
seen a few wake_ups in other stack traces which seem to be connected with
other deadlock.  Probably some sort of co-incidence.

Thanks,
NeilBrown

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