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Received: from mx1.redhat.com ([209.132.183.28]) by casper.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1grp3w-0004jW-HY for linux-arm-kernel@lists.infradead.org; Thu, 07 Feb 2019 19:10:18 +0000 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C3FF8C0669A8; Thu, 7 Feb 2019 19:10:13 +0000 (UTC) Received: from llong.com (dhcp-17-35.bos.redhat.com [10.18.17.35]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1846D17A75; Thu, 7 Feb 2019 19:10:06 +0000 (UTC) From: Waiman Long To: Peter Zijlstra , Ingo Molnar , Will Deacon , Thomas Gleixner Subject: [PATCH-tip 18/22] locking/rwsem: Make rwsem_spin_on_owner() return a tri-state value Date: Thu, 7 Feb 2019 14:07:22 -0500 Message-Id: <1549566446-27967-19-git-send-email-longman@redhat.com> In-Reply-To: <1549566446-27967-1-git-send-email-longman@redhat.com> References: <1549566446-27967-1-git-send-email-longman@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Thu, 07 Feb 2019 19:10:15 +0000 (UTC) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190207_191016_908484_B2FC98A6 X-CRM114-Status: GOOD ( 21.92 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, linux-xtensa@linux-xtensa.org, Davidlohr Bueso , linux-ia64@vger.kernel.org, Tim Chen , Arnd Bergmann , linux-sh@vger.kernel.org, linux-hexagon@vger.kernel.org, x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org, Linus Torvalds , Borislav Petkov , linux-alpha@vger.kernel.org, sparclinux@vger.kernel.org, Waiman Long , Andrew Morton , linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP This patch modifies rwsem_spin_on_owner() to return a tri-state value to better reflect the state of lock holder which enables us to make a better decision of what to do next. Signed-off-by: Waiman Long --- kernel/locking/rwsem-xadd.c | 25 +++++++++++++++++++------ kernel/locking/rwsem-xadd.h | 5 +++++ 2 files changed, 24 insertions(+), 6 deletions(-) diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index 21d462f..0a29aac 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -305,14 +305,24 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) } /* - * Return true only if we can still spin on the owner field of the rwsem. + * Return the folowing three values depending on the lock owner state. + * 1 when owner changes and no reader is detected yet. + * 0 when owner changes and the new owner may be a reader. + * -1 when optimistic spinning has to stop because either the owner stops + * running, is unknown, or its timeslice has been used up. */ -static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem) +enum owner_state { + OWNER_SPINNABLE = 1, + OWNER_READER = 0, + OWNER_NONSPINNABLE = -1, +}; + +static noinline enum owner_state rwsem_spin_on_owner(struct rw_semaphore *sem) { struct task_struct *owner = rwsem_get_owner(sem); if (!is_rwsem_owner_spinnable(owner)) - return false; + return OWNER_NONSPINNABLE; rcu_read_lock(); /* @@ -337,7 +347,7 @@ static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem) */ if (need_resched() || !owner_on_cpu(owner, sem)) { rcu_read_unlock(); - return false; + return OWNER_NONSPINNABLE; } cpu_relax(); @@ -348,7 +358,10 @@ static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem) * If there is a new owner or the owner is not set, we continue * spinning. */ - return is_rwsem_owner_spinnable(rwsem_get_owner(sem)); + owner = rwsem_get_owner(sem); + if (!is_rwsem_owner_spinnable(owner)) + return OWNER_NONSPINNABLE; + return is_rwsem_owner_reader(owner) ? OWNER_READER : OWNER_SPINNABLE; } static bool rwsem_optimistic_spin(struct rw_semaphore *sem, const long wlock) @@ -371,7 +384,7 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem, const long wlock) * 2) readers own the lock as we can't determine if they are * actively running or not. */ - while (rwsem_spin_on_owner(sem)) { + while (rwsem_spin_on_owner(sem) == OWNER_SPINNABLE) { /* * Try to acquire the lock */ diff --git a/kernel/locking/rwsem-xadd.h b/kernel/locking/rwsem-xadd.h index d54b5db..1de6f1e 100644 --- a/kernel/locking/rwsem-xadd.h +++ b/kernel/locking/rwsem-xadd.h @@ -200,6 +200,11 @@ static inline bool is_rwsem_owner_spinnable(struct task_struct *owner) return !((unsigned long)owner & RWSEM_ANONYMOUSLY_OWNED); } +static inline bool is_rwsem_owner_reader(struct task_struct *owner) +{ + return (unsigned long)owner & RWSEM_READER_OWNED; +} + /* * Return true if the rwsem is owned by a reader. */