Messages in this thread Patch in this message | | | Date | Thu, 28 Feb 2008 20:53:09 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] Remove never-migrates assumption from rcu_process_callbacks() |
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* 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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