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Message-ID: <20110208193650.GG2146@linux.vnet.ibm.com>
Date: Tue, 8 Feb 2011 11:36:50 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Mike Galbraith <efault@....de>
Cc: Milton Miller <miltonm@....com>,
Peter Zijlstra <peterz@...radead.org>,
akpm@...ux-foundation.org, Anton Blanchard <anton@...ba.org>,
xiaoguangrong@...fujitsu.com, mingo@...e.hu, jaxboe@...ionio.com,
npiggin@...il.com, JBeulich@...ell.com, rusty@...tcorp.com.au,
torvalds@...ux-foundation.org, benh@...nel.crashing.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3 v2] call_function_many: fix list delete vs add race
On Mon, Feb 07, 2011 at 09:12:54AM +0100, Mike Galbraith wrote:
> On Tue, 2011-02-01 at 20:17 -0800, Paul E. McKenney wrote:
>
> FWIW, my red headed stepchild (.32 xen cluster beast) with..
> smp-smp_call_function_many-fix-SMP-race (6dc1989)
> smp-consolidate-writes-in-smp_call_function_interrupt (225c8e0)
> smp-smp_call_function_many-fix-list-delete-vs-add-race (V2)
> smp-smp_call_function_many-handle-concurrent-clearing-of-mask (V2)
> smp-generic_smp_call_function_interrupt-additional-memory-order-tightening (below)
> ..has not experienced any IPI problems lately, nor have I been able to
> trigger anything beating up my box running normal x64_64 kernels.
>
> That's not saying much since my IPI woes were only the concurrent
> clearing variety, just letting you know that these patches have received
> (and are receiving) hefty thumpage.
Very good, I have added your Tested-by to my patch.
Thanx, Paul
> > ------------------------------------------------------------------------
> >
> > smp_call_function: additional memory-order tightening.
> >
> > The csd_lock() and csd_unlock() interaction guarantees that the
> > smp_call_function_many() function sees the results of interactions
> > with prior incarnations of the callback, so the check is not needed.
> > Instead, tighter memory ordering is required in the companion
> > generic_smp_call_function_interrupt() function to ensure proper
> > interaction with partially initialized callbacks.
> >
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> >
> > diff --git a/kernel/smp.c b/kernel/smp.c
> > index 064bb6e..e091905 100644
> > --- a/kernel/smp.c
> > +++ b/kernel/smp.c
> > @@ -182,7 +182,7 @@ void generic_smp_call_function_interrupt(void)
> >
> > /*
> > * Ensure entry is visible on call_function_queue after we have
> > - * entered the IPI. See comment in smp_call_function_many.
> > + * entered the IPI. See comment in smp_call_function_many
> > * If we don't have this, then we may miss an entry on the list
> > * and never get another IPI to process it.
> > */
> > @@ -209,13 +209,18 @@ void generic_smp_call_function_interrupt(void)
> > if (!cpumask_test_cpu(cpu, data->cpumask))
> > continue;
> >
> > - smp_rmb();
> > + smp_mb(); /* If we see our bit set above, we need to see */
> > + /* all the processing associated with the prior */
> > + /* incarnation of this callback. */
> >
> > if (atomic_read(&data->refs) == 0)
> > continue;
> >
> > + smp_rmb(); /* We need to read ->refs before we read either */
> > + /* ->csd.func and ->csd.info. */
> > +
> > func = data->csd.func; /* for later warn */
> > - data->csd.func(data->csd.info);
> > + func(data->csd.info);
> >
> > /*
> > * If the cpu mask is not still set then func enabled
>
>
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