Re: [Experimental CPU Hotplug PATCH] - Move migrate_all_tasks to CPU_DEAD handling

From: Srivatsa Vaddagiri <vatsa@in.ibm.com>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>,
	rusty@au1.ibm.com, 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>
Subject: Re: [Experimental CPU Hotplug PATCH] - Move migrate_all_tasks to CPU_DEAD handling
Date: Wed, 7 Apr 2004 10:31:11 +0530	[thread overview]
Message-ID: <20040407050111.GA10256@in.ibm.com> (raw)
In-Reply-To: <1081310073.5922.86.camel@bach>

On Wed, Apr 07, 2004 at 01:54:34PM +1000, Rusty Russell wrote:
> No, it really is required.
> 
> The stop_machine thread runs on the cpu, then kicks everyone else off,
> then does a complete() (in stop_machine.c:do_stop()).  Without this
> check, the complete() drags the sleeping process (which called
> stop_machine) onto the dying CPU.

Precisely. That's why I ended up adding this in cpu_down!!

+	/* Ensure that we are not runnable on dying cpu */
+	old_allowed = current->cpus_allowed;
+	tmp = CPU_MASK_ALL;
+	cpu_clear(cpu, tmp);
+	set_cpus_allowed(current, tmp);

I restore the mask though (under covers of lock_cpu_hotplug) before
returning from cpu_down. Task should never see this violated affinity.

Rusty,
	What do you think abt the whole patch? It has withstood 
my stress-test harness :-)

-- 

Thanks and Regards,
Srivatsa Vaddagiri,
Linux Technology Center,
IBM Software Labs,
Bangalore, INDIA - 560017