linux-kernel - Re: [-mm PATCH] RCU: debug sleep check

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Message-Id: <20060924144440.ca7e6464.akpm@osdl.org>
Date:	Sun, 24 Sep 2006 14:44:40 -0700
From:	Andrew Morton <akpm@...l.org>
To:	dipankar@...ibm.com
Cc:	linux-kernel@...r.kernel.org, Paul E McKenney <paulmck@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [-mm PATCH] RCU: debug sleep check

On Mon, 25 Sep 2006 03:05:08 +0530
Dipankar Sarma <dipankar@...ibm.com> wrote:

> On Sun, Sep 24, 2006 at 11:56:46AM -0700, Andrew Morton wrote:
> > On Mon, 25 Sep 2006 00:05:09 +0530
> > Dipankar Sarma <dipankar@...ibm.com> wrote:
> > 
> > > Add a debug check for rcu read-side critical section code calling
> > > a function that might sleep which is illegal. The check is enabled only
> > > if CONFIG_DEBUG_SPINLOCK_SLEEP is set.
> > > 
> > 
> > Does this actually change anything?  rcu_read_lock is preempt_disable(), and
> > might_sleep() already triggers if called inside preempt_disable().
> 
> It makes a difference if CONFIG_PREEMPT=n. AFAICS, preempt_disable()
> is a nop then and rcu needs its own check for sleeping while
> in read-side critical section.

Right.  I think enough people run with CONFIG_PREEMPT=y to make this
change rather unnecessary.

And if there are developers out there who are testing their code without an
effective CONFIG_DEBUG_SPINLOCK_SLEEP, then *that* is what we need to fix,
no?

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