From 1791f881435fab951939ad700e947b66c062e083 Mon Sep 17 00:00:00 2001 From: Richard Cochran Date: Wed, 30 Mar 2011 15:24:21 +0200 Subject: posix clocks: Replace mutex with reader/writer semaphore A dynamic posix clock is protected from asynchronous removal by a mutex. However, using a mutex has the unwanted effect that a long running clock operation in one process will unnecessarily block other processes. For example, one process might call read() to get an external time stamp coming in at one pulse per second. A second process calling clock_gettime would have to wait for almost a whole second. This patch fixes the issue by using a reader/writer semaphore instead of a mutex. Signed-off-by: Richard Cochran Cc: John Stultz Link: http://lkml.kernel.org/r/%3C20110330132421.GA31771%40riccoc20.at.omicron.at%3E Signed-off-by: Thomas Gleixner --- include/linux/posix-clock.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'include/linux/posix-clock.h') diff --git a/include/linux/posix-clock.h b/include/linux/posix-clock.h index 369e19d3750b..7f1183dcd119 100644 --- a/include/linux/posix-clock.h +++ b/include/linux/posix-clock.h @@ -24,6 +24,7 @@ #include #include #include +#include struct posix_clock; @@ -104,7 +105,7 @@ struct posix_clock_operations { * @ops: Functional interface to the clock * @cdev: Character device instance for this clock * @kref: Reference count. - * @mutex: Protects the 'zombie' field from concurrent access. + * @rwsem: Protects the 'zombie' field from concurrent access. * @zombie: If 'zombie' is true, then the hardware has disappeared. * @release: A function to free the structure when the reference count reaches * zero. May be NULL if structure is statically allocated. @@ -117,7 +118,7 @@ struct posix_clock { struct posix_clock_operations ops; struct cdev cdev; struct kref kref; - struct mutex mutex; + struct rw_semaphore rwsem; bool zombie; void (*release)(struct posix_clock *clk); }; -- cgit v1.2.3-59-g8ed1b