x86/irq: Retrieve irq data after locking irq_desc

irq_data is protected by irq_desc->lock, so retrieving the irq chip
from irq_data outside the lock is racy vs. an concurrent update. Move
it into the lock held region.

While at it add a comment why the vector walk does not require
vector_lock.

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/20150705171102.331320612@linutronix.de

1 files changed, 6 insertions, 1 deletions

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 85ca76e6241c..c7dfe1be784e 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -497,6 +497,11 @@ void fixup_irqs(void)
          */
         mdelay(1);
 
+        /*
+         * We can walk the vector array of this cpu without holding
+         * vector_lock because the cpu is already marked !online, so
+         * nothing else will touch it.
+         */
         for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS; vector++) {
                 unsigned int irr;
 
@@ -508,9 +513,9 @@ void fixup_irqs(void)
                         irq = __this_cpu_read(vector_irq[vector]);
 
                         desc = irq_to_desc(irq);
+                        raw_spin_lock(&desc->lock);
                         data = irq_desc_get_irq_data(desc);
                         chip = irq_data_get_irq_chip(data);
-                        raw_spin_lock(&desc->lock);
                         if (chip->irq_retrigger) {
                                 chip->irq_retrigger(data);
                                 __this_cpu_write(vector_irq[vector], VECTOR_RETRIGGERED);