Re: [PATCH] fix lock imbalances in /drivers/media/video/cafe_ccic.c

Re: [PATCH] fix lock imbalances in /drivers/media/video/cafe_ccic.c

[Daniel Walker]

On Thu, 2009-09-10 at 18:37 +0000, iceberg wrote:
> In ./drivers/media/video/cafe_ccic.c, in function cafe_pci_probe: 
> Mutex must be unlocked before exit
> 	1. On paths starting with mutex lock in line 1912, then continuing in lines: 
> 1929, 1936 (goto unreg) and 1940 (goto iounmap) . 
> 	2. On path starting in line 1971 mutex lock, and then continuing in line 1978 
> (goto out_smbus) mutex.
> 
> Fix lock imbalances in function cafe_pci_probe.
> Found by Linux Driver Verification project.

Could you run this through checkpatch and fix any issues you find? It
looks like you need to use tabs for indentation in a couple places.

Daniel

Re: [PATCH] fix lock imbalances in /drivers/media/video/cafe_ccic.c

[Jonathan Corbet]

On Thu, 10 Sep 2009 18:37:34 +0000
iceberg <strakh@ispras.ru> wrote:

> In ./drivers/media/video/cafe_ccic.c, in function cafe_pci_probe: 
> Mutex must be unlocked before exit
> 	1. On paths starting with mutex lock in line 1912, then continuing in lines: 
> 1929, 1936 (goto unreg) and 1940 (goto iounmap) . 
> 	2. On path starting in line 1971 mutex lock, and then continuing in line 1978 
> (goto out_smbus) mutex.

That's a definite bug, but I hate all those unlocks in the error
branches.  As it happens, we don't really need the mutex until the
device has been exposed to the rest of the kernel, so I propose the
following as a better patch.

Thanks for pointing this out,

jon

---
Fix a mutex leak

Certain error exits from cafe_pci_probe() can leave the camera mutex
locked.  For much of the time, we didn't need the mutex anyway; take it out
and add an unlock in the path where it is needed.

Reported-by: Alexander Strakh <strakh@ispras.ru>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
---
 drivers/media/video/cafe_ccic.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/drivers/media/video/cafe_ccic.c b/drivers/media/video/cafe_ccic.c
index c4d181d..0f62b5e 100644
--- a/drivers/media/video/cafe_ccic.c
+++ b/drivers/media/video/cafe_ccic.c
@@ -1909,7 +1909,6 @@ static int cafe_pci_probe(struct pci_dev *pdev,
 		goto out_free;
 
 	mutex_init(&cam->s_mutex);
-	mutex_lock(&cam->s_mutex);
 	spin_lock_init(&cam->dev_lock);
 	cam->state = S_NOTREADY;
 	cafe_set_config_needed(cam, 1);
@@ -1949,7 +1948,6 @@ static int cafe_pci_probe(struct pci_dev *pdev,
 	 * because the sensor could attach in this call chain, leading to
 	 * unsightly deadlocks.
 	 */
-	mutex_unlock(&cam->s_mutex);  /* attach can deadlock */
 	ret = cafe_smbus_setup(cam);
 	if (ret)
 		goto out_freeirq;
@@ -1991,6 +1989,7 @@ static int cafe_pci_probe(struct pci_dev *pdev,
 	return 0;
 
 out_smbus:
+	mutex_unlock(&cam->s_mutex);
 	cafe_smbus_shutdown(cam);
 out_freeirq:
 	cafe_ctlr_power_down(cam);
-- 
1.6.2.5

[PATCH] fix lock imbalances in /drivers/media/video/cafe_ccic.c

[iceberg]

In ./drivers/media/video/cafe_ccic.c, in function cafe_pci_probe: 
Mutex must be unlocked before exit
	1. On paths starting with mutex lock in line 1912, then continuing in lines: 
1929, 1936 (goto unreg) and 1940 (goto iounmap) . 
	2. On path starting in line 1971 mutex lock, and then continuing in line 1978 
(goto out_smbus) mutex.

Fix lock imbalances in function cafe_pci_probe.
Found by Linux Driver Verification project.

Signed-off-by: Alexander Strakh <strakh@ispras.ru>

---
diff --git a/./a/drivers/media/video/cafe_ccic.c 
b/./b/drivers/media/video/cafe_ccic.c
index c4d181d..2987433 100644
--- a/./a/drivers/media/video/cafe_ccic.c
+++ b/./b/drivers/media/video/cafe_ccic.c
@@ -1925,19 +1925,24 @@ static int cafe_pci_probe(struct pci_dev *pdev,
         * Get set up on the PCI bus.
         */
        ret = pci_enable_device(pdev);
-       if (ret)
+       if (ret) {
+               mutex_unlock(&cam->s_mutex);
                goto out_unreg;
+       }
        pci_set_master(pdev);

        ret = -EIO;
        cam->regs = pci_iomap(pdev, 0, 0);
        if (! cam->regs) {
                printk(KERN_ERR "Unable to ioremap cafe-ccic regs\n");
+               mutex_unlock(&cam->s_mutex);
                goto out_unreg;
        }
        ret = request_irq(pdev->irq, cafe_irq, IRQF_SHARED, "cafe-ccic", cam);
-       if (ret)
+       if (ret) {
+               mutex_unlock(&cam->s_mutex);
                goto out_iounmap;
+       }
        /*
         * Initialize the controller and leave it powered up.  It will
         * stay that way until the sensor driver shows up.
@@ -1974,8 +1979,10 @@ static int cafe_pci_probe(struct pci_dev *pdev,
 /*     cam->vdev.debug = V4L2_DEBUG_IOCTL_ARG;*/
        cam->vdev.v4l2_dev = &cam->v4l2_dev;
        ret = video_register_device(&cam->vdev, VFL_TYPE_GRABBER, -1);
-       if (ret)
+       if (ret) {
+               mutex_unlock(&cam->s_mutex);
                goto out_smbus;
+       }
        video_set_drvdata(&cam->vdev, cam);

        /*

Re: [PATCH] fix lock imbalances in /drivers/media/video/cafe_ccic.c

[Steven Rostedt]

On Thu, Sep 10, 2009 at 09:30:03AM -0600, Jonathan Corbet wrote:
> On Thu, 10 Sep 2009 18:37:34 +0000
> iceberg <strakh@ispras.ru> wrote:
> 
> > In ./drivers/media/video/cafe_ccic.c, in function cafe_pci_probe: 
> > Mutex must be unlocked before exit
> > 	1. On paths starting with mutex lock in line 1912, then continuing in lines: 
> > 1929, 1936 (goto unreg) and 1940 (goto iounmap) . 
> > 	2. On path starting in line 1971 mutex lock, and then continuing in line 1978 
> > (goto out_smbus) mutex.
> 
> That's a definite bug, but I hate all those unlocks in the error
> branches.  As it happens, we don't really need the mutex until the
> device has been exposed to the rest of the kernel, so I propose the
> following as a better patch.
> 
> Thanks for pointing this out,

Actually, for something like this, I would put the mutex_unlock in the error path,
and just add a local variable to tell that it is locked.

	int is_locked = 0;

[...]

	mutex_lock(&cam->s_mutex);
	is_locked = 1;

[...]

	mutex_unlock(&cam->s_mutex);
	is_locked = 0;

[...]

out_iounmap:
	pci_iounmap(pdev, cam->regs);
	if (is_locked)
		mutex_unlock(&cam->s_mutex);
out_free:

[...]

Or something similar. I hate the multiple unlocks too.

-- Steve

> 
> jon
> 
> ---
> Fix a mutex leak
> 
> Certain error exits from cafe_pci_probe() can leave the camera mutex
> locked.  For much of the time, we didn't need the mutex anyway; take it out
> and add an unlock in the path where it is needed.
> 
> Reported-by: Alexander Strakh <strakh@ispras.ru>
> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
> ---
>  drivers/media/video/cafe_ccic.c |    3 +--
>  1 files changed, 1 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/video/cafe_ccic.c b/drivers/media/video/cafe_ccic.c
> index c4d181d..0f62b5e 100644
> --- a/drivers/media/video/cafe_ccic.c
> +++ b/drivers/media/video/cafe_ccic.c
> @@ -1909,7 +1909,6 @@ static int cafe_pci_probe(struct pci_dev *pdev,
>  		goto out_free;
>  
>  	mutex_init(&cam->s_mutex);
> -	mutex_lock(&cam->s_mutex);
>  	spin_lock_init(&cam->dev_lock);
>  	cam->state = S_NOTREADY;
>  	cafe_set_config_needed(cam, 1);
> @@ -1949,7 +1948,6 @@ static int cafe_pci_probe(struct pci_dev *pdev,
>  	 * because the sensor could attach in this call chain, leading to
>  	 * unsightly deadlocks.
>  	 */
> -	mutex_unlock(&cam->s_mutex);  /* attach can deadlock */
>  	ret = cafe_smbus_setup(cam);
>  	if (ret)
>  		goto out_freeirq;
> @@ -1991,6 +1989,7 @@ static int cafe_pci_probe(struct pci_dev *pdev,
>  	return 0;
>  
>  out_smbus:
> +	mutex_unlock(&cam->s_mutex);
>  	cafe_smbus_shutdown(cam);
>  out_freeirq:
>  	cafe_ctlr_power_down(cam);
> -- 
> 1.6.2.5
> 
> --
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Re: [PATCH] fix lock imbalances in /drivers/media/video/cafe_ccic.c

[iceberg]

On Thursday 10 September 2009 15:30:03 you wrote:

	Incorrect patch. See path starting with "if (cam->sensor == null) {" in line 
1960. In this case we goto out_smbs and try mutex_unlock on unlocking mutex.

> On Thu, 10 Sep 2009 18:37:34 +0000
>
> iceberg <strakh@ispras.ru> wrote:
> > In ./drivers/media/video/cafe_ccic.c, in function cafe_pci_probe:
> > Mutex must be unlocked before exit
> > 	1. On paths starting with mutex lock in line 1912, then continuing in
> > lines: 1929, 1936 (goto unreg) and 1940 (goto iounmap) .
> > 	2. On path starting in line 1971 mutex lock, and then continuing in line
> > 1978 (goto out_smbus) mutex.
>
> That's a definite bug, but I hate all those unlocks in the error
> branches.  As it happens, we don't really need the mutex until the
> device has been exposed to the rest of the kernel, so I propose the
> following as a better patch.
>
> Thanks for pointing this out,
>
> jon
>
> ---
> Fix a mutex leak
>
> Certain error exits from cafe_pci_probe() can leave the camera mutex
> locked.  For much of the time, we didn't need the mutex anyway; take it out
> and add an unlock in the path where it is needed.
>
> Reported-by: Alexander Strakh <strakh@ispras.ru>
> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
> ---
>  drivers/media/video/cafe_ccic.c |    3 +--
>  1 files changed, 1 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/media/video/cafe_ccic.c
> b/drivers/media/video/cafe_ccic.c index c4d181d..0f62b5e 100644
> --- a/drivers/media/video/cafe_ccic.c
> +++ b/drivers/media/video/cafe_ccic.c
> @@ -1909,7 +1909,6 @@ static int cafe_pci_probe(struct pci_dev *pdev,
>  		goto out_free;
>
>  	mutex_init(&cam->s_mutex);
> -	mutex_lock(&cam->s_mutex);
>  	spin_lock_init(&cam->dev_lock);
>  	cam->state = S_NOTREADY;
>  	cafe_set_config_needed(cam, 1);
> @@ -1949,7 +1948,6 @@ static int cafe_pci_probe(struct pci_dev *pdev,
>  	 * because the sensor could attach in this call chain, leading to
>  	 * unsightly deadlocks.
>  	 */
> -	mutex_unlock(&cam->s_mutex);  /* attach can deadlock */
>  	ret = cafe_smbus_setup(cam);
>  	if (ret)
>  		goto out_freeirq;
> @@ -1991,6 +1989,7 @@ static int cafe_pci_probe(struct pci_dev *pdev,
>  	return 0;
>
>  out_smbus:
> +	mutex_unlock(&cam->s_mutex);
>  	cafe_smbus_shutdown(cam);
>  out_freeirq:
>  	cafe_ctlr_power_down(cam);