2013-06-20 16:18:23

by Vitalii Demianets

Subject: [PATCH char-misc-next] 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 <[email protected]>
---
drivers/uio/uio_pdrv_genirq.c | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/uio/uio_pdrv_genirq.c b/drivers/uio/uio_pdrv_genirq.c
index 9741549..bcd72f3 100644
--- 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);

--
1.7.12.4
--
With Best Regards,
Vitalii Demianets

2013-06-21 12:44:34

by Pavel Machek

Subject: Re: [PATCH char-misc-next] UIO: Fix concurrency issue

On Thu 2013-06-20 16:36:00, Vitalii Demianets wrote:
> 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 <[email protected]>

Sounds good.

Reviewed-by: Pavel Machek <[email protected]>

--
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