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

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 88b366487b0e44b613e83d412febfad74381ca92..85ca76e6241c64b38f1eda2ccdc6184bd2d8af2b 100644 (file)
--- 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++) {