x86/irq: Use proper locking in check_irq_vectors_for_cpu_disable()

It's unsafe to examine fields in the irq descriptor w/o holding the
descriptor lock. Add proper locking.

While at it add a comment why the vector check can run lock less

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: xiao jin <jin.xiao@intel.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Yanmin Zhang <yanmin_zhang@linux.intel.com>
Link: http://lkml.kernel.org/r/20150705171102.236544164@linutronix.de

1 files changed, 12 insertions, 1 deletions

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 88b366487b0e..85ca76e6241c 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -347,14 +347,22 @@ int check_irq_vectors_for_cpu_disable(void)
                         if (!desc)
                                 continue;
 
+                        /*
+                         * Protect against concurrent action removal,
+                         * affinity changes etc.
+                         */
+                        raw_spin_lock(&desc->lock);
                         data = irq_desc_get_irq_data(desc);
                         cpumask_copy(&affinity_new, data->affinity);
                         cpumask_clear_cpu(this_cpu, &affinity_new);
 
                         /* Do not count inactive or per-cpu irqs. */
-                        if (!irq_has_action(irq) || irqd_is_per_cpu(data))
+                        if (!irq_has_action(irq) || irqd_is_per_cpu(data)) {
+                                raw_spin_unlock(&desc->lock);
                                 continue;
+                        }
 
+                        raw_spin_unlock(&desc->lock);
                         /*
                          * A single irq may be mapped to multiple
                          * cpu's vector_irq[] (for example IOAPIC cluster
@@ -385,6 +393,9 @@ int check_irq_vectors_for_cpu_disable(void)
                  * vector. If the vector is marked in the used vectors
                  * bitmap or an irq is assigned to it, we don't count
                  * it as available.
+                 *
+                 * As this is an inaccurate snapshot anyway, we can do
+                 * this w/o holding vector_lock.
                  */
                 for (vector = FIRST_EXTERNAL_VECTOR;
                      vector < first_system_vector; vector++) {