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    Subject[PATCH 3.18-rc3 v9 2/5] 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

    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 | 26 +++++++++++++++++++-------
    1 file changed, 19 insertions(+), 7 deletions(-)

    diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
    index bb4bc20573ea..a53aa11e4f17 100644
    --- a/drivers/irqchip/irq-gic.c
    +++ b/drivers/irqchip/irq-gic.c
    @@ -75,8 +75,11 @@ 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 FIQ handlers and therefore
    + * must not be locked for writing when FIQs are enabled.
    */
    -static DEFINE_RAW_SPINLOCK(cpu_map_migration_lock);
    +static DEFINE_RWLOCK(cpu_map_migration_lock);

    /*
    * The GIC mapping of CPU interfaces does not necessarily match
    @@ -625,12 +628,20 @@ 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 read locks 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;

    - raw_spin_lock_irqsave(&cpu_map_migration_lock, flags);
    + read_lock(&cpu_map_migration_lock);

    /* Convert our logical CPU mask into a physical one. */
    for_each_cpu(cpu, mask)
    @@ -645,7 +656,7 @@ 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);

    - raw_spin_unlock_irqrestore(&cpu_map_migration_lock, flags);
    + read_unlock(&cpu_map_migration_lock);
    }
    #endif

    @@ -693,7 +704,8 @@ 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)
    {
    @@ -724,9 +736,9 @@ 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
    --
    1.9.3


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