Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965203AbbBBV7t (ORCPT ); Mon, 2 Feb 2015 16:59:49 -0500 Received: from g2t2353.austin.hp.com ([15.217.128.52]:54915 "EHLO g2t2353.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753697AbbBBV7o (ORCPT ); Mon, 2 Feb 2015 16:59:44 -0500 From: Jason Low To: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org Cc: Davidlohr Bueso , Tim Chen , "Paul E. McKenney" , Linus Torvalds , tglx@linutronix.de, chegu_vinod@hp.com, Aswin Chandramouleeswaran , Jason Low Subject: [PATCH 2/2] mutex: Refactor mutex_spin_on_owner Date: Mon, 2 Feb 2015 13:59:27 -0800 Message-Id: <1422914367-5574-3-git-send-email-jason.low2@hp.com> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: <1422914367-5574-1-git-send-email-jason.low2@hp.com> References: <1422914367-5574-1-git-send-email-jason.low2@hp.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3042 Lines: 99 As suggested by Davidlohr, we could refactor mutex_spin_on_owner(). Currently, we split up owner_running() with mutex_spin_on_owner(). When the owner changes, we make duplicate owner checks which are not necessary. It also makes the code a bit obscure as we are using a second check to figure out why we broke out of the loop. This patch modifies it such that we remove the owner_running() function and the mutex_spin_on_owner loop directly checks for if the owner changes, if the owner is not running, or if we need to reschedule. If the owner changes, we break out of the loop and return true. If the owner is not running or if we need to reschedule, then break out of the loop and return false. Cc: Davidlohr Bueso Signed-off-by: Jason Low --- kernel/locking/mutex.c | 47 ++++++++++++++++++++++------------------------- 1 files changed, 22 insertions(+), 25 deletions(-) diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 04ea9ce..218c561 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -204,44 +204,41 @@ ww_mutex_set_context_fastpath(struct ww_mutex *lock, * Mutex spinning code migrated from kernel/sched/core.c */ -static inline bool owner_running(struct mutex *lock, struct task_struct *owner) -{ - if (lock->owner != owner) - return false; - - /* - * Ensure we emit the owner->on_cpu, dereference _after_ checking - * lock->owner still matches owner, if that fails, owner might - * point to free()d memory, if it still matches, the rcu_read_lock() - * ensures the memory stays valid. - */ - barrier(); - - return owner->on_cpu; -} - /* * Look out! "owner" is an entirely speculative pointer * access and not reliable. */ static noinline -int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner) +bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner) { + bool ret; + rcu_read_lock(); - while (owner_running(lock, owner)) { - if (need_resched()) + while (true) { + /* Return success when the lock owner changed */ + if (lock->owner != owner) { + ret = true; break; + } + + /* + * Ensure we emit the owner->on_cpu, dereference _after_ + * checking lock->owner still matches owner, if that fails, + * owner might point to free()d memory, if it still matches, + * the rcu_read_lock() ensures the memory stays valid. + */ + barrier(); + + if (!owner->on_cpu || need_resched()) { + ret = false; + break; + } cpu_relax_lowlatency(); } rcu_read_unlock(); - /* - * We break out of the loop above on either need_resched(), when - * the owner is not running, or when the lock owner changed. - * Return success only when the lock owner changed. - */ - return lock->owner != owner; + return ret; } /* -- 1.7.2.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/