From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Rostedt Subject: [PATCH RT 03/25] rtmutex: Simplify rtmutex_slowtrylock() Date: Fri, 13 Mar 2015 11:18:28 -0400 Message-ID: <20150313151834.646837400@goodmis.org> References: <20150313151825.583263173@goodmis.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Cc: Thomas Gleixner , Carsten Emde , Sebastian Andrzej Siewior , John Kacur , Paul Gortmaker , Oleg Nesterov , Lai Jiangshan To: linux-kernel@vger.kernel.org, linux-rt-users Return-path: Content-Disposition: inline; filename=0003-rtmutex-Simplify-rtmutex_slowtrylock.patch Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-rt-users.vger.kernel.org 3.2.68-rt99-rc1 stable review patch. If anyone has any objections, please let me know. ------------------ From: Thomas Gleixner upstream-commit: 88f2b4c15e561bb5c28709d666364f273bf54b98 Oleg noticed that rtmutex_slowtrylock() has a pointless check for rt_mutex_owner(lock) != current. To avoid calling try_to_take_rtmutex() we really want to check whether the lock has an owner at all or whether the trylock failed because the owner is NULL, but the RT_MUTEX_HAS_WAITERS bit is set. This covers the lock is owned by caller situation as well. We can actually do this check lockless. trylock is taking a chance whether we take lock->wait_lock to do the check or not. Add comments to the function while at it. Reported-by: Oleg Nesterov Signed-off-by: Thomas Gleixner Reviewed-by: Steven Rostedt Reviewed-by: Lai Jiangshan Signed-off-by: Steven Rostedt Conflicts: kernel/rtmutex.c --- kernel/rtmutex.c | 33 +++++++++++++++++++++------------ 1 file changed, 21 insertions(+), 12 deletions(-) diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c index 972ec87bd1d9..d19060236770 100644 --- a/kernel/rtmutex.c +++ b/kernel/rtmutex.c @@ -1275,24 +1275,33 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state, /* * Slow path try-lock function: */ -static inline int -rt_mutex_slowtrylock(struct rt_mutex *lock) +static inline int rt_mutex_slowtrylock(struct rt_mutex *lock) { - int ret = 0; + int ret; + /* + * If the lock already has an owner we fail to get the lock. + * This can be done without taking the @lock->wait_lock as + * it is only being read, and this is a trylock anyway. + */ + if (rt_mutex_owner(lock)) + return 0; + + /* + * The mutex has currently no owner. Lock the wait lock and + * try to acquire the lock. + */ if (!raw_spin_trylock(&lock->wait_lock)) - return ret; + return 0; init_lists(lock); - if (likely(rt_mutex_owner(lock) != current)) { + ret = try_to_take_rt_mutex(lock, current, NULL); - ret = try_to_take_rt_mutex(lock, current, NULL); - /* - * try_to_take_rt_mutex() sets the lock waiters - * bit unconditionally. Clean this up. - */ - fixup_rt_mutex_waiters(lock); - } + /* + * try_to_take_rt_mutex() sets the lock waiters bit + * unconditionally. Clean this up. + */ + fixup_rt_mutex_waiters(lock); raw_spin_unlock(&lock->wait_lock); -- 2.1.4