linux-kernel - [PATCH 1/2] of: fix race when matching drivers

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Date:	Wed, 18 May 2011 13:21:00 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	devicetree-discuss@...ts.ozlabs.org, gregkh@...e.de,
	linux-kernel@...r.kernel.org, Milton Miller <miltonm@....com>,
	sparclinux@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Josip Rodin <joy@...uzijast.net>
Subject: [PATCH 1/2] of: fix race when matching drivers

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

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);

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