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Subject[RESEND PATCH 4.0-rc7 v20 2/6] irqchip: gic: Make gic_raise_softirq FIQ-safe
Date
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

arch/arm/ uses IPIs to implement arch_irq_work_raise(), thus this issue
renders it difficult for FIQ handlers to safely defer work to less
restrictive calling contexts.

This patch fixes the problem by converting the cpu_map_migration_lock
into a rwlock making it safe to re-enter the function.

Note that 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>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
---
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 a181b836d5ea..578ffc5ec087 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 gic_migration_lock(unsigned long *flags)
+static inline void gic_migration_lock(void)
{
- raw_spin_lock_irqsave(&cpu_map_migration_lock, *flags);
+ read_lock(&cpu_map_migration_lock);
}

-static inline void gic_migration_unlock(unsigned long flags)
+static inline void gic_migration_unlock(void)
{
- raw_spin_unlock_irqrestore(&cpu_map_migration_lock, flags);
+ read_unlock(&cpu_map_migration_lock);
}
#else
-static inline void gic_migration_lock(unsigned long *flags) {}
-static inline void gic_migration_unlock(unsigned long flags) {}
+static inline void gic_migration_lock(void) {}
+static inline void gic_migration_unlock(void) {}
#endif

/*
@@ -647,12 +650,20 @@ 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 gic_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;

- gic_migration_lock(&flags);
+ gic_migration_lock();

/* Convert our logical CPU mask into a physical one. */
for_each_cpu(cpu, mask)
@@ -667,7 +678,7 @@ 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);

- gic_migration_unlock(flags);
+ gic_migration_unlock();
}
#endif

@@ -715,7 +726,8 @@ 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)
{
@@ -746,9 +758,9 @@ 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
--
2.1.0


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