Subject: Re: [Experimental CPU Hotplug PATCH] - Move migrate_all_tasks to
	CPU_DEAD handling
From: Rusty Russell <rusty@rustcorp.com.au>
To: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>, Ingo Molnar <mingo@elte.hu>,
       Andrew Morton <akpm@osdl.org>,
       lkml - Kernel Mailing List <linux-kernel@vger.kernel.org>,
       LHCS list <lhcs-devel@lists.sourceforge.net>,
       Joel Schopp <jschopp@austin.ibm.com>
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On Thu, 2004-04-08 at 00:17, Srivatsa Vaddagiri wrote:
> On Wed, Apr 07, 2004 at 03:32:12PM +1000, Rusty Russell wrote:
> > But other tasks can do a getaffinity() on it and see the wrong affinity.
> > Probably not a big issue.
> 
> hmm .. the fact that getaffinity reads the cpus_allowed mask w/o doing
> lock_cpu_hotplug makes it already racy wrt setaffinity?

But that's OK: that's a user race.  It's like reading a file at the same
time as writing it.

> Maybe it needs to take CPU hotplug sem before it reads the mask?

Yes, taking it in both syscalls would work, too.

> I would like to run my stress tests for longer time before I send it
> for inclusion (i would be on vacation till next tuesday ..so maybe i will send
> in the patch after that!)

Thanks.  BTW, can you take a look at the FIXME: in xics.c and change it
to be dynamic.  Joel is having trouble proving it's a problem, and yet
Anton assures me that ioremap is needed, so CPUs not present at boot
which are brought in should be failing...

Thanks!
Rusty.
-- 
Anyone who quotes me in their signature is an idiot -- Rusty Russell

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