linux-kernel - Re: [PATCH 1/3 v2] call_function_many: fix list delete vs add race

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Sun, 21 Aug 2011 08:17:11 +0200
From:	Mike Galbraith <efault@....de>
To:	paulmck@...ux.vnet.ibm.com
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 Tue, 2011-02-08 at 11:36 -0800, Paul E. McKenney wrote:
> 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.

I'm still using your barrier changes.  Is it safe to drop them?  HA
clusters falling over is _not_ something I want to risk resurrecting by
dropping them just because they didn't go anywhere.
 
> 
> 							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
> > 
> > 


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/