linux-kernel - Re: [PATCH] fix lock imbalances in /drivers/media/video/cafe

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Message-ID: <20090910093003.194c300f@bike.lwn.net>
Date:	Thu, 10 Sep 2009 09:30:03 -0600
From:	Jonathan Corbet <corbet@....net>
To:	iceberg <strakh@...ras.ru>
Cc:	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fix lock imbalances in /drivers/media/video/cafe_ccic.c

On Thu, 10 Sep 2009 18:37:34 +0000
iceberg <strakh@...ras.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@...ras.ru>
Signed-off-by: Jonathan Corbet <corbet@....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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