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SubjectRe: [PATCH] Fix hibernate/resume in presence of PREEMPT_RCU and hotplug
On Thu, Feb 28, 2008 at 10:35:08AM +0530, Gautham R Shenoy wrote:
> 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!

I wonder as well. In fact there is (at least) one other such bug,
submitting patch separately. :-/

Thanx, Paul

> 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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