Re: [PATCH]CPU hotplug breaks wake_up_new_task
From: Srivatsa Vaddagiri (vatsa_at_in.ibm.com)
Date: 05/31/05
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Date: Tue, 31 May 2005 15:10:45 +0530 To: Shaohua Li <shaohua.li@intel.com>
On Tue, May 31, 2005 at 07:29:39AM +0000, Shaohua Li wrote:
> Hi,
> There is a race condition at wake_up_new_task at CPU hotplug case.
> Say do_fork
> copy_process (which sets new forked task's current cpu, cpu_allowed)
> <-------- the new forked task's current cpu is offline
> wake_up_new_task
> wake_up_new_task will put the forked task into a dead cpu.
This was noticed/fixed long back. Apparently somebody has reintroduced
the bug. The simple fix for this race is:
--- kernel/fork.c.org 2005-05-31 14:57:15.000000000 +0530
+++ kernel/fork.c 2005-05-31 15:07:20.000000000 +0530
@@ -1024,8 +1024,7 @@ static task_t *copy_process(unsigned lon
* parent's CPU). This avoids alot of nasty races.
*/
p->cpus_allowed = current->cpus_allowed;
- if (unlikely(!cpu_isset(task_cpu(p), p->cpus_allowed)))
- set_task_cpu(p, smp_processor_id());
+ set_task_cpu(p, smp_processor_id());
/*
* Check for pending SIGKILL! The new thread should not be allowed
Could you test and check if it avoids whatever problem you are seeing?
-- Thanks and Regards, Srivatsa Vaddagiri, Linux Technology Center, IBM Software Labs, Bangalore, INDIA - 560017 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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