On Wed, Nov 20, 2013 at 11:21:07AM +0100, Nicholas Mc Guire wrote:
> From 46393dc3185026c8500c2b734747d7c8785f3dc9 Mon Sep 17 00:00:00 2001
> From: Nicholas Mc Guire <der.herr@xxxxxxx>
> Date: Tue, 19 Nov 2013 23:31:05 -0500
> Subject: [PATCH 1/2] remove recursive call to migrate_disable in read_lock_bh
>
> read_lock_bh/read_unlock_bh unconditionally calls local_bh_disable/enable
> which already does a migrate_disable/enable - no need for this recursive call.
>
> patch is on top of 3.12-rt2
>
> No change of functionality
>
> Signed-off-by: Nicholas Mc Guire <der.herr@xxxxxxx>
> ---
> include/linux/rwlock_rt.h | 2 --
> 1 files changed, 0 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/rwlock_rt.h b/include/linux/rwlock_rt.h
> index 853ee36..87f5a1d 100644
> --- a/include/linux/rwlock_rt.h
> +++ b/include/linux/rwlock_rt.h
> @@ -53,7 +53,6 @@ extern void __rt_rwlock_init(rwlock_t *rwlock, char *name, struct lock_class_key
> #define read_lock_bh(lock) \
> do { \
> local_bh_disable(); \
> - migrate_disable(); \
> rt_read_lock(lock); \
> } while (0)
>
> @@ -83,7 +82,6 @@ extern void __rt_rwlock_init(rwlock_t *rwlock, char *name, struct lock_class_key
> #define read_unlock_bh(lock) \
> do { \
> rt_read_unlock(lock); \
> - migrate_enable(); \
> local_bh_enable(); \
> } while (0)
So the problem with this patch and the next is that:
read_lock_bh();
read_unlock();
local_bh_enable();
Is a valid pattern; and you'll notice that the release part has 2
migrate put refs. So if you can make a patch similar to:
lkml.kernel.org/r/20131120162736.624493595@xxxxxxxxxxxxx
That allows read_lock_bh() to obtain 2 migrate disable refs in one go,
then it would all work out just fine.
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