genirq: Fix race in register_irq_proc()

Per-IRQ directories in procfs are created only when a handler is first
added to the irqdesc, not when the irqdesc is created.  In the case of
a shared IRQ, multiple tasks can race to create a directory.  This
race condition seems to have been present forever, but is easier to
hit with async probing.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Link: http://lkml.kernel.org/r/1443266636.2004.2.camel@decadent.org.uk
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org

diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index e3a8c9577ba641c38747a0925a7896eca7ef4d79..a50ddc9417ff5fbdccf837f9f43b716200ceb013 100644 (file)
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -12,6 +12,7 @@
 #include <linux/seq_file.h>
 #include <linux/interrupt.h>
 #include <linux/kernel_stat.h>
+#include <linux/mutex.h>
 
 #include "internals.h"
 
@@ -323,18 +324,29 @@ void register_handler_proc(unsigned int irq, struct irqaction *action)
 
 void register_irq_proc(unsigned int irq, struct irq_desc *desc)
 {
+       static DEFINE_MUTEX(register_lock);
        char name [MAX_NAMELEN];
 
-       if (!root_irq_dir || (desc->irq_data.chip == &no_irq_chip) || desc->dir)
+       if (!root_irq_dir || (desc->irq_data.chip == &no_irq_chip))
                return;
 
+       /*
+        * irq directories are registered only when a handler is
+        * added, not when the descriptor is created, so multiple
+        * tasks might try to register at the same time.
+        */
+       mutex_lock(&register_lock);
+
+       if (desc->dir)
+               goto out_unlock;
+
        memset(name, 0, MAX_NAMELEN);
        sprintf(name, "%d", irq);
 
        /* create /proc/irq/1234 */
        desc->dir = proc_mkdir(name, root_irq_dir);
        if (!desc->dir)
-               return;
+               goto out_unlock;
 
 #ifdef CONFIG_SMP
        /* create /proc/irq/<irq>/smp_affinity */
@@ -355,6 +367,9 @@ void register_irq_proc(unsigned int irq, struct irq_desc *desc)
 
        proc_create_data("spurious", 0444, desc->dir,
                         &irq_spurious_proc_fops, (void *)(long)irq);
+
+out_unlock:
+       mutex_unlock(&register_lock);
 }
 
 void unregister_irq_proc(unsigned int irq, struct irq_desc *desc)