linux-kernel - Re: [PATCH] rcu: Improve detection of illegal synchronize

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Message-ID: <20120105021758.GS2448@linux.vnet.ibm.com>
Date:	Wed, 4 Jan 2012 18:17:58 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Sasha Levin <levinsasha928@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rcu: Improve detection of illegal synchronize_rcu() call
 from RCU read side

On Thu, Jan 05, 2012 at 03:06:03AM +0100, Frederic Weisbecker wrote:
> On Wed, Jan 04, 2012 at 06:01:08PM -0800, Paul E. McKenney wrote:
> > On Thu, Jan 05, 2012 at 02:45:20AM +0100, Frederic Weisbecker wrote:
> > > On Wed, Jan 04, 2012 at 01:30:35PM -0800, Paul E. McKenney wrote:
> > > > On Wed, Jan 04, 2012 at 08:03:39PM +0100, Frederic Weisbecker wrote:
> > > > > Actually for the case of RCU, the wait_for_completion() called by synchronize_rcu()

[ . . . ]

> > > > > rcutiny seems to be fine with the cond_resched() call, but srcu needs
> > > > > a special treatment.
> > > > 
> > > > For the moment, I just applied rcu_lockdep_assert() everywhere -- zero
> > > > cost on non-lockdep kernels, and fully handles all of the RCU simple
> > > > self-deadlock cases.
> > > 
> > > So, for RCU I'm not sure this is useful given the might_sleep() things.
> > > But for srcu it is.
> > 
> > One nice thing about the lockdep approach is that it tracks where the
> > conflicting RCU read-side critical section started.  But I am planning
> > for these to be 3.4 material, so we do have some time to refine them.
> 
> Yeah sure. And in any case it's still good to keep might_sleep() early
> to spot other sources of illegal atomic sections (irqs disabled and co)

Agreed!

							Thanx, Paul

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