UIO: Fix concurrency issue

In a SMP case there was a race condition issue between
uio_pdrv_genirq_irqcontrol() running on one CPU and irq handler on
another CPU. Fix it by spin_locking shared resources access inside irq
handler.  Also:
  - Change disable_irq to disable_irq_nosync to avoid deadlock, because
    disable_irq waits for the completion of the irq handler;
  - Change atomic bit-manipulation routines to their non-atomic
    counterparts as we already are guarding the code by spinlock.

Signed-off-by: Vitalii Demianets <vitas@nppfactor.kiev.ua>
Reviewed-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/uio/uio_pdrv_genirq.c b/drivers/uio/uio_pdrv_genirq.c
index 97415492779ea3e499c4d6a7378efde786428537..bcd72f3a62c3a735816493e512e63eb3917fbbc8 100644 (file)
--- a/drivers/uio/uio_pdrv_genirq.c
+++ b/drivers/uio/uio_pdrv_genirq.c
@@ -37,6 +37,11 @@ struct uio_pdrv_genirq_platdata {
        struct platform_device *pdev;
 };
 
+/* Bits in uio_pdrv_genirq_platdata.flags */
+enum {
+       UIO_IRQ_DISABLED = 0,
+};
+
 static int uio_pdrv_genirq_open(struct uio_info *info, struct inode *inode)
 {
        struct uio_pdrv_genirq_platdata *priv = info->priv;
@@ -63,8 +68,10 @@ static irqreturn_t uio_pdrv_genirq_handler(int irq, struct uio_info *dev_info)
         * remember the state so we can allow user space to enable it later.
         */
 
-       if (!test_and_set_bit(0, &priv->flags))
+       spin_lock(&priv->lock);
+       if (!__test_and_set_bit(UIO_IRQ_DISABLED, &priv->flags))
                disable_irq_nosync(irq);
+       spin_unlock(&priv->lock);
 
        return IRQ_HANDLED;
 }
@@ -78,16 +85,17 @@ static int uio_pdrv_genirq_irqcontrol(struct uio_info *dev_info, s32 irq_on)
         * in the interrupt controller, but keep track of the
         * state to prevent per-irq depth damage.
         *
-        * Serialize this operation to support multiple tasks.
+        * Serialize this operation to support multiple tasks and concurrency
+        * with irq handler on SMP systems.
         */
 
        spin_lock_irqsave(&priv->lock, flags);
        if (irq_on) {
-               if (test_and_clear_bit(0, &priv->flags))
+               if (__test_and_clear_bit(UIO_IRQ_DISABLED, &priv->flags))
                        enable_irq(dev_info->irq);
        } else {
-               if (!test_and_set_bit(0, &priv->flags))
-                       disable_irq(dev_info->irq);
+               if (!__test_and_set_bit(UIO_IRQ_DISABLED, &priv->flags))
+                       disable_irq_nosync(dev_info->irq);
        }
        spin_unlock_irqrestore(&priv->lock, flags);