Re: [PATCH] migrate_disable pushd down in rt_read_trylock

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

* Sebastian Andrzej Siewior | 2013-11-29 16:14:01 [+0100]:

>* Nicholas Mc Guire | 2013-11-23 01:51:58 [+0100]:
>
>>>From 5c9a0c1510ec29c1e148f66f3c111f52f7565df1 Mon Sep 17 00:00:00 2001
>>From: Nicholas Mc Guire <der.herr@hofr.at>
>>Date: Fri, 22 Nov 2013 02:41:48 -0500
>>Subject: [PATCH] migrate_disable pushd down in rt_read_trylock
>>
>> No need to migrate_disable before requesting the lock and no need to 
>> speculatively disable/enable on every recursive call. migration_disable 
>> can be done at the latest point in the code before returning an acquired 
>> ``lock.
>>
>> patch is on top of 3.12-rt2
>>
>> No change of functionality
>Applied without this line.

and dropped because there is a problem with this:
- Now 
  if you read_lock() and then read_try_lock() then migrate_disable() is
  called by each caller. Also on read_unlock() migrate_enable() is called
  by each caller.

- with patch
  read_lock() calls migrate_disable() and read_try_lock() does not. Both
  get the lock. So on read_unlock(), the read_try_lock() owner remains
  unbalanced.

disabling migration prior incrementing read_depth should fix this.

>>Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>

Sebastian