genirq: Delegate irq affinity setting to the irq thread

irq_set_thread_affinity() calls set_cpus_allowed_ptr() which might
sleep, but irq_set_thread_affinity() is called with desc->lock held
and can be called from hard interrupt context as well. The code has
another bug as it does not hold a ref on the task struct as required
by set_cpus_allowed_ptr().

Just set the IRQTF_AFFINITY bit in action->thread_flags. The next time
the thread runs it migrates itself. Solves all of the above problems
nicely.

Add kerneldoc to irq_set_thread_affinity() while at it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <new-submission>

1 files changed, 44 insertions, 6 deletions

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 50da67672901..f0de36f13a44 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -80,14 +80,22 @@ int irq_can_set_affinity(unsigned int irq)
         return 1;
 }
 
-void
-irq_set_thread_affinity(struct irq_desc *desc, const struct cpumask *cpumask)
+/**
+ *      irq_set_thread_affinity - Notify irq threads to adjust affinity
+ *      @desc:          irq descriptor which has affitnity changed
+ *
+ *      We just set IRQTF_AFFINITY and delegate the affinity setting
+ *      to the interrupt thread itself. We can not call
+ *      set_cpus_allowed_ptr() here as we hold desc->lock and this
+ *      code can be called from hard interrupt context.
+ */
+void irq_set_thread_affinity(struct irq_desc *desc)
 {
         struct irqaction *action = desc->action;
 
         while (action) {
                 if (action->thread)
-                        set_cpus_allowed_ptr(action->thread, cpumask);
+                        set_bit(IRQTF_AFFINITY, &action->thread_flags);
                 action = action->next;
         }
 }
@@ -112,7 +120,7 @@ int irq_set_affinity(unsigned int irq, const struct cpumask *cpumask)
         if (desc->status & IRQ_MOVE_PCNTXT) {
                 if (!desc->chip->set_affinity(irq, cpumask)) {
                         cpumask_copy(desc->affinity, cpumask);
-                        irq_set_thread_affinity(desc, cpumask);
+                        irq_set_thread_affinity(desc);
                 }
         }
         else {
@@ -122,7 +130,7 @@ int irq_set_affinity(unsigned int irq, const struct cpumask *cpumask)
 #else
         if (!desc->chip->set_affinity(irq, cpumask)) {
                 cpumask_copy(desc->affinity, cpumask);
-                irq_set_thread_affinity(desc, cpumask);
+                irq_set_thread_affinity(desc);
         }
 #endif
         desc->status |= IRQ_AFFINITY_SET;
@@ -176,7 +184,7 @@ int irq_select_affinity_usr(unsigned int irq)
         spin_lock_irqsave(&desc->lock, flags);
         ret = setup_affinity(irq, desc);
         if (!ret)
-                irq_set_thread_affinity(desc, desc->affinity);
+                irq_set_thread_affinity(desc);
         spin_unlock_irqrestore(&desc->lock, flags);
 
         return ret;
@@ -444,6 +452,34 @@ static int irq_wait_for_interrupt(struct irqaction *action)
 }
 
 /*
+ * Check whether we need to change the affinity of the interrupt thread.
+ */
+static void
+irq_thread_check_affinity(struct irq_desc *desc, struct irqaction *action)
+{
+        cpumask_var_t mask;
+
+        if (!test_and_clear_bit(IRQTF_AFFINITY, &action->thread_flags))
+                return;
+
+        /*
+         * In case we are out of memory we set IRQTF_AFFINITY again and
+         * try again next time
+         */
+        if (!alloc_cpumask_var(&mask, GFP_KERNEL)) {
+                set_bit(IRQTF_AFFINITY, &action->thread_flags);
+                return;
+        }
+
+        spin_lock_irq(&desc->lock);
+        cpumask_copy(mask, desc->affinity);
+        spin_unlock_irq(&desc->lock);
+
+        set_cpus_allowed_ptr(current, mask);
+        free_cpumask_var(mask);
+}
+
+/*
  * Interrupt handler thread
  */
 static int irq_thread(void *data)
@@ -458,6 +494,8 @@ static int irq_thread(void *data)
 
         while (!irq_wait_for_interrupt(action)) {
 
+                irq_thread_check_affinity(desc, action);
+
                 atomic_inc(&desc->threads_active);
 
                 spin_lock_irq(&desc->lock);