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SubjectRe: [PATCH] Remove never-migrates assumption from rcu_process_callbacks()

* Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:

> Hello again!
>
> This patch fixes a potentially invalid access to a per-CPU variable in
> rcu_process_callbacks(). This per-CPU access needs to be done in such
> a way as to guarantee that the code using it cannot move to some other
> CPU before all uses of the value accessed have completed. Even though
> this code is currently only invoked from softirq context, which
> currrently cannot migrate to some other CPU, life would be better if
> this code did not silently make such an assumption.

i've got the patch below queued up already - same thing, right?

Ingo

----------->
Subject: rcupreempt: fix hibernate/resume in presence of PREEMPT_RCU and hotplug
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date: Wed, 27 Feb 2008 16:21:10 -0800
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.

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>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/rcupreempt.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
Index: linux/kernel/rcupreempt.c
===================================================================
--- linux.orig/kernel/rcupreempt.c
+++ linux/kernel/rcupreempt.c
@@ -918,8 +918,9 @@ 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;

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