From d8e2a4053574002135fbb032c2e74f1d1dbb2103 Mon Sep 17 00:00:00 2001 From: Nicholas Piggin Date: Wed, 9 Aug 2017 22:41:22 +1000 Subject: [PATCH] powerpc/watchdog: Improve watchdog lock primitive - Hard-disable interrupts before taking the lock, which prevents soft-NMI re-entrancy and therefore can prevent deadlocks. - Use raw_ variants of local_irq_disable to avoid irq debugging. - When the lock is contended, spin at low SMT priority, using loads only, and with interrupts enabled (where possible). Some stalls have been noticed at high loads that go away with improved locking. There should not be so much locking contention in the first place (which is addressed in a subsequent patch), but locking should still be improved. Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman --- arch/powerpc/kernel/watchdog.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c index b67f8b03a32d..fda4d044d326 100644 --- a/arch/powerpc/kernel/watchdog.c +++ b/arch/powerpc/kernel/watchdog.c @@ -71,15 +71,20 @@ static inline void wd_smp_lock(unsigned long *flags) * This may be called from low level interrupt handlers at some * point in future. */ - local_irq_save(*flags); - while (unlikely(test_and_set_bit_lock(0, &__wd_smp_lock))) - cpu_relax(); + raw_local_irq_save(*flags); + hard_irq_disable(); /* Make it soft-NMI safe */ + while (unlikely(test_and_set_bit_lock(0, &__wd_smp_lock))) { + raw_local_irq_restore(*flags); + spin_until_cond(!test_bit(0, &__wd_smp_lock)); + raw_local_irq_save(*flags); + hard_irq_disable(); + } } static inline void wd_smp_unlock(unsigned long *flags) { clear_bit_unlock(0, &__wd_smp_lock); - local_irq_restore(*flags); + raw_local_irq_restore(*flags); } static void wd_lockup_ipi(struct pt_regs *regs) -- 2.20.1