From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6534EC282CE for ; Fri, 5 Apr 2019 19:22:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3559721738 for ; Fri, 5 Apr 2019 19:22:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731942AbfDETWX (ORCPT ); Fri, 5 Apr 2019 15:22:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:15966 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731922AbfDETWV (ORCPT ); Fri, 5 Apr 2019 15:22:21 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id ECA083087BA1; Fri, 5 Apr 2019 19:22:20 +0000 (UTC) Received: from llong.com (dhcp-17-47.bos.redhat.com [10.18.17.47]) by smtp.corp.redhat.com (Postfix) with ESMTP id A175561367; Fri, 5 Apr 2019 19:22:19 +0000 (UTC) From: Waiman Long To: Peter Zijlstra , Ingo Molnar , Will Deacon , Thomas Gleixner Cc: linux-kernel@vger.kernel.org, x86@kernel.org, Davidlohr Bueso , Linus Torvalds , Tim Chen , Waiman Long Subject: [PATCH-tip v2 09/12] locking/rwsem: Add more rwsem owner access helpers Date: Fri, 5 Apr 2019 15:21:12 -0400 Message-Id: <20190405192115.17416-10-longman@redhat.com> In-Reply-To: <20190405192115.17416-1-longman@redhat.com> References: <20190405192115.17416-1-longman@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Fri, 05 Apr 2019 19:22:21 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Before combining owner and count, we are adding two new helpers for accessing the owner value in the rwsem. 1) struct task_struct *rwsem_get_owner(struct rw_semaphore *sem) 2) bool is_rwsem_reader_owned(struct rw_semaphore *sem) Signed-off-by: Waiman Long --- kernel/locking/rwsem-xadd.c | 15 ++++++++++----- kernel/locking/rwsem.c | 3 +-- kernel/locking/rwsem.h | 32 ++++++++++++++++++++++++++------ 3 files changed, 37 insertions(+), 13 deletions(-) diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index bc3fd14cf354..a9756e3e3a73 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -312,7 +312,7 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) preempt_disable(); rcu_read_lock(); - owner = READ_ONCE(sem->owner); + owner = rwsem_get_owner(sem); if (owner) { ret = is_rwsem_owner_spinnable(owner) && (is_rwsem_owner_reader(owner) || owner_on_cpu(owner)); @@ -344,15 +344,21 @@ enum owner_state { static noinline enum owner_state rwsem_spin_on_owner(struct rw_semaphore *sem) { - struct task_struct *owner = READ_ONCE(sem->owner); + struct task_struct *owner = rwsem_get_owner(sem); long count; if (!is_rwsem_owner_spinnable(owner)) return OWNER_NONSPINNABLE; rcu_read_lock(); - while (owner && !is_rwsem_owner_reader(owner) - && (READ_ONCE(sem->owner) == owner)) { + while (owner && !is_rwsem_owner_reader(owner)) { + struct task_struct *new_owner = rwsem_get_owner(sem); + + if (new_owner != owner) { + owner = new_owner; + break; /* The owner has changed */ + } + /* * Ensure we emit the owner->on_cpu, dereference _after_ * checking sem->owner still matches owner, if that fails, @@ -379,7 +385,6 @@ static noinline enum owner_state rwsem_spin_on_owner(struct rw_semaphore *sem) * spinning except when here is no active locks and the handoff bit * is set. In this case, we have to stop spinning. */ - owner = READ_ONCE(sem->owner); if (!is_rwsem_owner_spinnable(owner)) return OWNER_NONSPINNABLE; if (owner && !is_rwsem_owner_reader(owner)) diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index ccbf18f560ff..38d24676e01c 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -198,8 +198,7 @@ EXPORT_SYMBOL(down_write_killable_nested); void up_read_non_owner(struct rw_semaphore *sem) { - DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & RWSEM_READER_OWNED), - sem); + DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); __up_read(sem); } diff --git a/kernel/locking/rwsem.h b/kernel/locking/rwsem.h index 1398799b7547..bbb8a266dd50 100644 --- a/kernel/locking/rwsem.h +++ b/kernel/locking/rwsem.h @@ -92,6 +92,11 @@ static inline void rwsem_clear_owner(struct rw_semaphore *sem) WRITE_ONCE(sem->owner, NULL); } +static inline struct task_struct *rwsem_get_owner(struct rw_semaphore *sem) +{ + return READ_ONCE(sem->owner); +} + /* * The task_struct pointer of the last owning reader will be left in * the owner field. @@ -136,6 +141,23 @@ static inline bool is_rwsem_spinnable(struct rw_semaphore *sem) return is_rwsem_owner_spinnable(READ_ONCE(sem->owner)); } +/* + * Return true if the rwsem is owned by a reader. + */ +static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem) +{ +#ifdef CONFIG_DEBUG_RWSEMS + /* + * Check the count to see if it is write-locked. + */ + long count = atomic_long_read(&sem->count); + + if (count & RWSEM_WRITER_MASK) + return false; +#endif + return (unsigned long)sem->owner & RWSEM_READER_OWNED; +} + /* * Return true if rwsem is owned by an anonymous writer or readers. */ @@ -156,6 +178,7 @@ static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem) { unsigned long val = (unsigned long)current | RWSEM_READER_OWNED | RWSEM_ANONYMOUSLY_OWNED; + if (READ_ONCE(sem->owner) == (struct task_struct *)val) cmpxchg_relaxed((unsigned long *)&sem->owner, val, RWSEM_READER_OWNED | RWSEM_ANONYMOUSLY_OWNED); @@ -218,8 +241,7 @@ static inline void __down_read(struct rw_semaphore *sem) if (unlikely(atomic_long_fetch_add_acquire(RWSEM_READER_BIAS, &sem->count) & RWSEM_READ_FAILED_MASK)) { rwsem_down_read_failed(sem); - DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & - RWSEM_READER_OWNED), sem); + DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); } else { rwsem_set_reader_owned(sem); } @@ -231,8 +253,7 @@ static inline int __down_read_killable(struct rw_semaphore *sem) &sem->count) & RWSEM_READ_FAILED_MASK)) { if (IS_ERR(rwsem_down_read_failed_killable(sem))) return -EINTR; - DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & - RWSEM_READER_OWNED), sem); + DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); } else { rwsem_set_reader_owned(sem); } @@ -299,8 +320,7 @@ static inline void __up_read(struct rw_semaphore *sem) { long tmp; - DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & RWSEM_READER_OWNED), - sem); + DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); rwsem_clear_reader_owned(sem); tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count); if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) -- 2.18.1