linux-kernel - Re: [1/4] rcu: Detect uses of rcu read side in extended quiescent states

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Date:	Fri, 10 Jun 2011 01:58:42 -0700
From:	Michel Lespinasse <walken@...gle.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Milton Miller <miltonm@....com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [1/4] rcu: Detect uses of rcu read side in extended quiescent states

On Mon, Jun 6, 2011 at 6:36 PM, Frederic Weisbecker <fweisbec@...il.com> wrote:
> Ok but that only improves the rcu debugging. What about instead improving
> might_sleep() to also work in !PREEMPT, so that it profits to any detection
> of forbidden sleeping (sleep inside spinlock, preempt_disable, might_fault, etc...)
>
> We could define a new config:
>
> config PREEMPT_COUNT
>       default PREEMPT || DEBUG_SPINLOCK_SLEEP
>
> and build preempt_disable()/preempt_enable() on top of that instead
> of using CONFIG_PREEMPT directly.
>
> Does that look sane?

Yes, I think this would be helpful.

I actually sent out a patch for that about a year ago - message title
was "Stronger CONFIG_DEBUG_SPINLOCK_SLEEP without CONFIG_PREEMPT".
However that code has rotted since, and my attempt at a trivial port
ended up spewing complaints in dmesg at boot time...

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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