Messages in this thread | | | Date | Fri, 31 Aug 2012 16:51:57 -0700 | From | Josh Triplett <> | Subject | Re: [PATCH tip/core/rcu 10/26] rcu: Exit RCU extended QS on kernel preemption after irq/exception |
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On Thu, Aug 30, 2012 at 02:05:27PM -0700, Paul E. McKenney wrote: > From: Frederic Weisbecker <fweisbec@gmail.com> > > When an exception or an irq exits, and we are going to resume into > interrupted kernel code, the low level architecture code calls > preempt_schedule_irq() if there is a need to reschedule. > > If the interrupt/exception occured between a call to rcu_user_enter() > (from syscall exit, exception exit, do_notify_resume exit, ...) and > a real resume to userspace (iret,...), preempt_schedule_irq() can be > called whereas RCU thinks we are in userspace. But preempt_schedule_irq() > is going to run kernel code and may be some RCU read side critical > section. We must exit the userspace extended quiescent state before > we call it. > > To solve this, just call rcu_user_exit() in the beginning of > preempt_schedule_irq(). > > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> > Cc: Alessio Igor Bogani <abogani@kernel.org> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Avi Kivity <avi@redhat.com> > Cc: Chris Metcalf <cmetcalf@tilera.com> > Cc: Christoph Lameter <cl@linux.com> > Cc: Geoff Levand <geoff@infradead.org> > Cc: Gilad Ben Yossef <gilad@benyossef.com> > Cc: Hakan Akkan <hakanakkan@gmail.com> > Cc: H. Peter Anvin <hpa@zytor.com> > Cc: Ingo Molnar <mingo@kernel.org> > Cc: Josh Triplett <josh@joshtriplett.org> > Cc: Kevin Hilman <khilman@ti.com> > Cc: Max Krasnyansky <maxk@qualcomm.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Stephen Hemminger <shemminger@vyatta.com> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
> kernel/sched/core.c | 1 + > 1 files changed, 1 insertions(+), 0 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 07c6d9a..0bd599b 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3564,6 +3564,7 @@ asmlinkage void __sched preempt_schedule_irq(void) > /* Catch callers which need to be fixed */ > BUG_ON(ti->preempt_count || !irqs_disabled()); > > + rcu_user_exit(); > do { > add_preempt_count(PREEMPT_ACTIVE); > local_irq_enable(); > -- > 1.7.8 >
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