Patchwork [1/2] of: fix race when matching drivers

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Submitter Grant Likely
Date May 18, 2011, 7:21 p.m.
Message ID <20110518192100.28986.94335.stgit@ponder>
Download mbox | patch
Permalink /patch/96219/
State Not Applicable
Delegated to: David Miller
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Comments

Grant Likely - May 18, 2011, 7:21 p.m.
From: Milton Miller <miltonm@bga.com>

If two drivers are probing devices at the same time, both will write
their match table result to the dev->of_match cache at the same time.

Only write the result if the device matches.

In a thread titled "SBus devices sometimes detected, sometimes not",
Meelis reported his SBus hme was not detected about 50% of the time.
>From the debug suggested by Grant it was obvious another driver matched
some devices between the call to match the hme and the hme discovery
failling.

Reported-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Milton Miller <miltonm@bga.com>
[grant.likely: modified to only call of_match_device() once]
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
---
 include/linux/of_device.h |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)


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gregkh@suse.de - May 18, 2011, 7:54 p.m.
On Wed, May 18, 2011 at 01:21:00PM -0600, Grant Likely wrote:
> From: Milton Miller <miltonm@bga.com>
> 
> If two drivers are probing devices at the same time, both will write
> their match table result to the dev->of_match cache at the same time.
> 
> Only write the result if the device matches.
> 
> In a thread titled "SBus devices sometimes detected, sometimes not",
> Meelis reported his SBus hme was not detected about 50% of the time.
> >From the debug suggested by Grant it was obvious another driver matched
> some devices between the call to match the hme and the hme discovery
> failling.
> 
> Reported-by: Meelis Roos <mroos@linux.ee>
> Signed-off-by: Milton Miller <miltonm@bga.com>
> [grant.likely: modified to only call of_match_device() once]
> Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

Acked-by: Greg Kroah-Hartman <gregkh@suse.de>

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David Miller - May 18, 2011, 9:03 p.m.
From: Grant Likely <grant.likely@secretlab.ca>
Date: Wed, 18 May 2011 13:21:00 -0600

> From: Milton Miller <miltonm@bga.com>
> 
> If two drivers are probing devices at the same time, both will write
> their match table result to the dev->of_match cache at the same time.
> 
> Only write the result if the device matches.
> 
> In a thread titled "SBus devices sometimes detected, sometimes not",
> Meelis reported his SBus hme was not detected about 50% of the time.
>>From the debug suggested by Grant it was obvious another driver matched
> some devices between the call to match the hme and the hme discovery
> failling.
> 
> Reported-by: Meelis Roos <mroos@linux.ee>
> Signed-off-by: Milton Miller <miltonm@bga.com>
> [grant.likely: modified to only call of_match_device() once]
> Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

Tested on SunBlade2500 and Niagara2+

Acked-by: David S. Miller <davem@davemloft.net>
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Patch

diff --git a/include/linux/of_device.h b/include/linux/of_device.h
index 8bfe6c1..b33d688 100644
--- a/include/linux/of_device.h
+++ b/include/linux/of_device.h
@@ -21,8 +21,12 @@  extern void of_device_make_bus_id(struct device *dev);
 static inline int of_driver_match_device(struct device *dev,
 					 const struct device_driver *drv)
 {
-	dev->of_match = of_match_device(drv->of_match_table, dev);
-	return dev->of_match != NULL;
+	const struct of_device_id *match;
+
+	match = of_match_device(drv->of_match_table, dev);
+	if (match)
+		dev->of_match = match;
+	return match != NULL;
 }
 
 extern struct platform_device *of_dev_get(struct platform_device *dev);