It is currently possible for FIQ handlers to re-enter gic_raise_softirq() and lock up.
gic_raise_softirq() lock(x); -~-> FIQ handle_fiq() gic_raise_softirq() lock(x); <-- Lockup
Calling printk() from a FIQ handler can trigger this problem because printk() raises an IPI when it needs to wake_up_klogd(). More generally, IPIs are the only means for FIQ handlers to safely defer work to less restrictive calling context so the function to raise them really needs to be FIQ-safe.
This patch fixes the problem by converting the cpu_map_migration_lock into a rwlock making it safe to re-enter the function.
Having made it safe to re-enter gic_raise_softirq() we no longer need to mask interrupts during gic_raise_softirq() because the b.L migration is always performed from task context.
Signed-off-by: Daniel Thompson daniel.thompson@linaro.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Jason Cooper jason@lakedaemon.net Cc: Russell King linux@arm.linux.org.uk Cc: Marc Zyngier marc.zyngier@arm.com --- drivers/irqchip/irq-gic.c | 38 +++++++++++++++++++++++++------------- 1 file changed, 25 insertions(+), 13 deletions(-)
diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c index e875da93f24a..5d72823bc5e9 100644 --- a/drivers/irqchip/irq-gic.c +++ b/drivers/irqchip/irq-gic.c @@ -75,22 +75,25 @@ static DEFINE_RAW_SPINLOCK(irq_controller_lock); /* * This lock is used by the big.LITTLE migration code to ensure no IPIs * can be pended on the old core after the map has been updated. + * + * This lock may be locked for reading from both IRQ and FIQ handlers + * and therefore must not be locked for writing when these are enabled. */ #ifdef CONFIG_BL_SWITCHER -static DEFINE_RAW_SPINLOCK(cpu_map_migration_lock); +static DEFINE_RWLOCK(cpu_map_migration_lock);
-static inline void bl_migration_lock(unsigned long *flags) +static inline void bl_migration_lock(void) { - raw_spin_lock_irqsave(&cpu_map_migration_lock, *flags); + read_lock(&cpu_map_migration_lock); }
-static inline void bl_migration_unlock(unsigned long flags) +static inline void bl_migration_unlock(void) { - raw_spin_unlock_irqrestore(&cpu_map_migration_lock, flags); + read_unlock(&cpu_map_migration_lock); } #else -static inline void bl_migration_lock(unsigned long *flags) {} -static inline void bl_migration_unlock(unsigned long flags) {} +static inline void bl_migration_lock(void) {} +static inline void bl_migration_unlock(void) {} #endif
/* @@ -640,12 +643,20 @@ static void __init gic_pm_init(struct gic_chip_data *gic) #endif
#ifdef CONFIG_SMP +/* + * Raise the specified IPI on all cpus set in mask. + * + * This function is safe to call from all calling contexts, including + * FIQ handlers. It relies on bl_migration_lock() being multiply acquirable + * to avoid deadlocks when the function is re-entered at different + * exception levels. + */ static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq) { int cpu; - unsigned long flags, map = 0; + unsigned long map = 0;
- bl_migration_lock(&flags); + bl_migration_lock();
/* Convert our logical CPU mask into a physical one. */ for_each_cpu(cpu, mask) @@ -660,7 +671,7 @@ static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq) /* this always happens on GIC0 */ writel_relaxed(map << 16 | irq, gic_data_dist_base(&gic_data[0]) + GIC_DIST_SOFTINT);
- bl_migration_unlock(flags); + bl_migration_unlock(); } #endif
@@ -708,7 +719,8 @@ int gic_get_cpu_id(unsigned int cpu) * Migrate all peripheral interrupts with a target matching the current CPU * to the interface corresponding to @new_cpu_id. The CPU interface mapping * is also updated. Targets to other CPU interfaces are unchanged. - * This must be called with IRQs locally disabled. + * This must be called from a task context and with IRQ and FIQ locally + * disabled. */ void gic_migrate_target(unsigned int new_cpu_id) { @@ -739,9 +751,9 @@ void gic_migrate_target(unsigned int new_cpu_id) * pending on the old cpu static. That means we can defer the * migration until after we have released the irq_controller_lock. */ - raw_spin_lock(&cpu_map_migration_lock); + write_lock(&cpu_map_migration_lock); gic_cpu_map[cpu] = 1 << new_cpu_id; - raw_spin_unlock(&cpu_map_migration_lock); + write_unlock(&cpu_map_migration_lock);
/* * Find all the peripheral interrupts targetting the current