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DateThu, 28 Feb 2008 10:35:08 +0530
FromGautham R Shenoy <>
SubjectRe: [PATCH] Fix hibernate/resume in presence of PREEMPT_RCU and hotplug
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On Wed, Feb 27, 2008 at 04:21:10PM -0800, Paul E. McKenney wrote:
Hello!

This fixes a oops encountered when doing hibernate/resume in presence of PREEMPT_RCU. The problem was that the code failed to disable preemption when accessing a per-CPU variable. This is OK when called from code that already has preemption disabled, but such is not the case from the suspend/resume code path.

Well, rcu_offline_cpu() is called from the cpu-offline callback path, and AFAICS, it doesn't disable preemption.

I wonder how we're seeing this only now! Indeed a good catch!
Reviewed-by: Gautham R Shenoy <ego@in.ibm.com>

Reported-by: Dave Young <hidave.darkstar@gmail.com> Tested-by: Dave Young <hidave.darkstar@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> ---

rcupreempt.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff -urpNa -X dontdiff linux-2.6.25-rc3/kernel/rcupreempt.c linux-2.6.25-rc3-rcuoffline/kernel/rcupreempt.c --- linux-2.6.25-rc3/kernel/rcupreempt.c 2008-02-26 16:58:43.000000000 -0800 +++ linux-2.6.25-rc3-rcuoffline/kernel/rcupreempt.c 2008-02-26 17:04:17.000000000 -0800 @@ -702,8 +702,9 @@ void rcu_offline_cpu(int cpu)
* fix.
*/

+ local_irq_save(flags);
rdp = RCU_DATA_ME();
- spin_lock_irqsave(&rdp->lock, flags);
+ spin_lock(&rdp->lock);
*rdp->nexttail = list;
if (list)
rdp->nexttail = tail;

-- 
Thanks and Regards
gautham


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