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
(cherry picked from commit 09cf92b784fae6109450c5d64f9908066d605249)

Orabug: 25671838

Signed-off-by: Ethan Zhao <ethan.zhao@oracle.com>
Reviewed-by: Jack Vogel <jack.vogel@oracle.com>

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index a87068edd01bb56f5a5545ee1c1100a1c1c33ac3..48c3aaa22133b053f8b7f8acd72715c1674824c4 100644 (file)
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -455,6 +455,11 @@ 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;
 
@@ -466,9 +471,9 @@ 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);