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

From: Grant Likely
Date: Wed May 18 2011 - 15:21:16 EST

From: Milton Miller <miltonm@xxxxxxx>

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

Reported-by: Meelis Roos <mroos@xxxxxxxx>
Signed-off-by: Milton Miller <miltonm@xxxxxxx>
[grant.likely: modified to only call of_match_device() once]
Signed-off-by: Grant Likely <grant.likely@xxxxxxxxxxxx>
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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