4.2.8-ckt2 -stable review patch. If anyone has any objections, please let me know.
---8<------------------------------------------------------------
From: Alistair Popple <alistair@xxxxxxxxxxxx>
commit 036592fbbe753d236402a0ae68148e7c143a0f0e upstream.
Commit 25642e1459ac ("powerpc/opal-irqchip: Fix double endian
conversion") fixed an endian bug by calling opal_handle_events() in
opal_event_unmask().
However this introduced a deadlock if we find an event is active
during unmasking and call opal_handle_events() again. The bad call
sequence is:
opal_interrupt()
-> opal_handle_events()
-> generic_handle_irq()
-> handle_level_irq()
-> raw_spin_lock(&desc->lock)
handle_irq_event(desc)
unmask_irq(desc)
-> opal_event_unmask()
-> opal_handle_events()
-> generic_handle_irq()
-> handle_level_irq()
-> raw_spin_lock(&desc->lock) (BOOM)
When generating multiple opal events in quick succession this would lead
to the following stall warnings:
EEH: Fenced PHB#0 detected, location: U78C9.001.WZS09XA-P1-C32
INFO: rcu_sched detected stalls on CPUs/tasks:
12-...: (1 GPs behind) idle=68f/140000000000001/0 softirq=860/861 fqs=2065
15-...: (1 GPs behind) idle=be5/140000000000001/0 softirq=1142/1143 fqs=2065
(detected by 13, t=2102 jiffies, g=1325, c=1324, q=602)
NMI watchdog: BUG: soft lockup - CPU#18 stuck for 22s! [irqbalance:2696]
INFO: rcu_sched detected stalls on CPUs/tasks:
12-...: (1 GPs behind) idle=68f/140000000000001/0 softirq=860/861 fqs=8371
15-...: (1 GPs behind) idle=be5/140000000000001/0 softirq=1142/1143 fqs=8371
(detected by 20, t=8407 jiffies, g=1325, c=1324, q=1290)
This patch corrects the problem by queuing the work if an event is
active during unmasking, which is similar to the pre-endian fix
behaviour.
Fixes: 25642e1459ac ("powerpc/opal-irqchip: Fix double endian conversion")
Signed-off-by: Alistair Popple <alistair@xxxxxxxxxxxx>
Reported-by: Andrew Donnellan <andrew.donnellan@xxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
---
arch/powerpc/platforms/powernv/opal-irqchip.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/platforms/powernv/opal-irqchip.c b/arch/powerpc/platforms/powernv/opal-irqchip.c
index b056bc0..ccabec5 100644
--- a/arch/powerpc/platforms/powernv/opal-irqchip.c
+++ b/arch/powerpc/platforms/powernv/opal-irqchip.c
@@ -83,7 +83,19 @@ static void opal_event_unmask(struct irq_data *d)
set_bit(d->hwirq, &opal_event_irqchip.mask);
opal_poll_events(&events);
- opal_handle_events(be64_to_cpu(events));
+ last_outstanding_events = be64_to_cpu(events);
+
+ /*
+ * We can't just handle the events now with opal_handle_events().
+ * If we did we would deadlock when opal_event_unmask() is called from
+ * handle_level_irq() with the irq descriptor lock held, because
+ * calling opal_handle_events() would call generic_handle_irq() and
+ * then handle_level_irq() which would try to take the descriptor lock
+ * again. Instead queue the events for later.
+ */
+ if (last_outstanding_events & opal_event_irqchip.mask)
+ /* Need to retrigger the interrupt */
+ irq_work_queue(&opal_event_irq_work);
}
static int opal_event_set_type(struct irq_data *d, unsigned int flow_type)
--
1.9.1
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