genirq/affinity: Defer affinity setting if irq chip is busy

The case that interrupt affinity setting fails with -EBUSY can be handled
in the kernel completely by using the already available generic pending
infrastructure.

If a irq_chip::set_affinity() fails with -EBUSY, handle it like the
interrupts for which irq_chip::set_affinity() can only be invoked from
interrupt context. Copy the new affinity mask to irq_desc::pending_mask and
set the affinity pending bit. The next raised interrupt for the affected
irq will check the pending bit and try to set the new affinity from the
handler. This avoids that -EBUSY is returned when an affinity change is
requested from user space and the previous change has not been cleaned
up. The new affinity will take effect when the next interrupt is raised
from the device.

Fixes: dccfe314 ("x86/vector: Simplify vector move cleanup")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Song Liu <songliubraving@fb.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <liu.song.a23@gmail.com>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: stable@vger.kernel.org
Cc: Mike Travis <mike.travis@hpe.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Tariq Toukan <tariqt@mellanox.com>
Link: https://lkml.kernel.org/r/20180604162224.819273597@linutronix.de

kernel/irq/manage.c

@@ -204,6 +204,39 @@ int irq_do_set_affinity(struct irq_data *data, const struct cpumask *mask,
 	return ret;
 }
 
+#ifdef CONFIG_GENERIC_PENDING_IRQ
+static inline int irq_set_affinity_pending(struct irq_data *data,
+					   const struct cpumask *dest)
+{
+	struct irq_desc *desc = irq_data_to_desc(data);
+
+	irqd_set_move_pending(data);
+	irq_copy_pending(desc, dest);
+	return 0;
+}
+#else
+static inline int irq_set_affinity_pending(struct irq_data *data,
+					   const struct cpumask *dest)
+{
+	return -EBUSY;
+}
+#endif
+
+static int irq_try_set_affinity(struct irq_data *data,
+				const struct cpumask *dest, bool force)
+{
+	int ret = irq_do_set_affinity(data, dest, force);
+
+	/*
+	 * In case that the underlying vector management is busy and the
+	 * architecture supports the generic pending mechanism then utilize
+	 * this to avoid returning an error to user space.
+	 */
+	if (ret == -EBUSY && !force)
+		ret = irq_set_affinity_pending(data, dest);
+	return ret;
+}
+
 int irq_set_affinity_locked(struct irq_data *data, const struct cpumask *mask,
 			    bool force)
 {
@@ -214,8 +247,8 @@ int irq_set_affinity_locked(struct irq_data *data, const struct cpumask *mask,
 	if (!chip || !chip->irq_set_affinity)
 		return -EINVAL;
 
-	if (irq_can_move_pcntxt(data)) {
-		ret = irq_do_set_affinity(data, mask, force);
+	if (irq_can_move_pcntxt(data) && !irqd_is_setaffinity_pending(data)) {
+		ret = irq_try_set_affinity(data, mask, force);
 	} else {
 		irqd_set_move_pending(data);
 		irq_copy_pending(desc, mask);