From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: [PATCH RFC tip/core/rcu 12/15] lib/assoc_array: Remove smp_read_barrier_depends() Date: Mon, 9 Oct 2017 17:22:46 -0700 Message-ID: <1507594969-8347-12-git-send-email-paulmck@linux.vnet.ibm.com> References: <20171010001951.GA6476@linux.vnet.ibm.com> Return-path: In-Reply-To: <20171010001951.GA6476@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, torvalds@linux-foundation.org, mark.rutland@arm.com, dhowells@redhat.com, linux-arch@vger.kernel.org, peterz@infradead.org, will.deacon@arm.com, "Paul E. McKenney" , Jonathan Corbet , Alexander Kuleshov List-Id: linux-arch.vger.kernel.org Now that smp_read_barrier_depends() is implied by READ_ONCE(), adding READ_ONCE() to assoc_array_ptr_to_leaf() and __assoc_array_ptr_to_meta() allows the several smp_read_barrier_depends() calls to be removed from lib/assoc_array.c. This commit makes this change. Signed-off-by: Paul E. McKenney Cc: Jonathan Corbet Cc: Mark Rutland Cc: Alexander Kuleshov --- include/linux/assoc_array_priv.h | 5 +++-- lib/assoc_array.c | 20 ++------------------ 2 files changed, 5 insertions(+), 20 deletions(-) diff --git a/include/linux/assoc_array_priv.h b/include/linux/assoc_array_priv.h index 711275e6681c..b47308bf1f99 100644 --- a/include/linux/assoc_array_priv.h +++ b/include/linux/assoc_array_priv.h @@ -135,13 +135,14 @@ static inline bool assoc_array_ptr_is_node(const struct assoc_array_ptr *x) static inline void *assoc_array_ptr_to_leaf(const struct assoc_array_ptr *x) { - return (void *)((unsigned long)x & ~ASSOC_ARRAY_PTR_TYPE_MASK); + return (void *)((unsigned long)READ_ONCE(x) & /* Address dependency. */ + ~ASSOC_ARRAY_PTR_TYPE_MASK); } static inline unsigned long __assoc_array_ptr_to_meta(const struct assoc_array_ptr *x) { - return (unsigned long)x & + return (unsigned long)READ_ONCE(x) & /* Address dependency. */ ~(ASSOC_ARRAY_PTR_SUBTYPE_MASK | ASSOC_ARRAY_PTR_TYPE_MASK); } static inline diff --git a/lib/assoc_array.c b/lib/assoc_array.c index fe7953aead82..52845f5cbf19 100644 --- a/lib/assoc_array.c +++ b/lib/assoc_array.c @@ -38,12 +38,10 @@ static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root, if (assoc_array_ptr_is_shortcut(cursor)) { /* Descend through a shortcut */ shortcut = assoc_array_ptr_to_shortcut(cursor); - smp_read_barrier_depends(); cursor = READ_ONCE(shortcut->next_node); } node = assoc_array_ptr_to_node(cursor); - smp_read_barrier_depends(); slot = 0; /* We perform two passes of each node. @@ -55,15 +53,9 @@ static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root, */ has_meta = 0; for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) { - ptr = READ_ONCE(node->slots[slot]); + ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */ has_meta |= (unsigned long)ptr; if (ptr && assoc_array_ptr_is_leaf(ptr)) { - /* We need a barrier between the read of the pointer - * and dereferencing the pointer - but only if we are - * actually going to dereference it. - */ - smp_read_barrier_depends(); - /* Invoke the callback */ ret = iterator(assoc_array_ptr_to_leaf(ptr), iterator_data); @@ -86,8 +78,6 @@ static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root, continue_node: node = assoc_array_ptr_to_node(cursor); - smp_read_barrier_depends(); - for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) { ptr = READ_ONCE(node->slots[slot]); if (assoc_array_ptr_is_meta(ptr)) { @@ -105,7 +95,6 @@ static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root, if (assoc_array_ptr_is_shortcut(parent)) { shortcut = assoc_array_ptr_to_shortcut(parent); - smp_read_barrier_depends(); cursor = parent; parent = READ_ONCE(shortcut->back_pointer); slot = shortcut->parent_slot; @@ -216,8 +205,6 @@ assoc_array_walk(const struct assoc_array *array, consider_node: node = assoc_array_ptr_to_node(cursor); - smp_read_barrier_depends(); - slot = segments >> (level & ASSOC_ARRAY_KEY_CHUNK_MASK); slot &= ASSOC_ARRAY_FAN_MASK; ptr = READ_ONCE(node->slots[slot]); @@ -254,7 +241,6 @@ assoc_array_walk(const struct assoc_array *array, cursor = ptr; follow_shortcut: shortcut = assoc_array_ptr_to_shortcut(cursor); - smp_read_barrier_depends(); pr_devel("shortcut to %d\n", shortcut->skip_to_level); sc_level = level + ASSOC_ARRAY_LEVEL_STEP; BUG_ON(sc_level > shortcut->skip_to_level); @@ -330,8 +316,7 @@ void *assoc_array_find(const struct assoc_array *array, assoc_array_walk_found_terminal_node) return NULL; - node = result.terminal_node.node; - smp_read_barrier_depends(); + node = READ_ONCE(result.terminal_node.node); /* Address dependency. */ /* If the target key is available to us, it's has to be pointed to by * the terminal node. @@ -344,7 +329,6 @@ void *assoc_array_find(const struct assoc_array *array, * actually going to dereference it. */ leaf = assoc_array_ptr_to_leaf(ptr); - smp_read_barrier_depends(); if (ops->compare_object(leaf, index_key)) return (void *)leaf; } -- 2.5.2 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:57866 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755805AbdJJAWz (ORCPT ); Mon, 9 Oct 2017 20:22:55 -0400 Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v9A0JPC4075527 for ; Mon, 9 Oct 2017 20:22:55 -0400 Received: from e15.ny.us.ibm.com (e15.ny.us.ibm.com [129.33.205.205]) by mx0b-001b2d01.pphosted.com with ESMTP id 2dgk2jsc3n-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 09 Oct 2017 20:22:55 -0400 Received: from localhost by e15.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 9 Oct 2017 20:22:54 -0400 From: "Paul E. McKenney" Subject: [PATCH RFC tip/core/rcu 12/15] lib/assoc_array: Remove smp_read_barrier_depends() Date: Mon, 9 Oct 2017 17:22:46 -0700 In-Reply-To: <20171010001951.GA6476@linux.vnet.ibm.com> References: <20171010001951.GA6476@linux.vnet.ibm.com> Message-ID: <1507594969-8347-12-git-send-email-paulmck@linux.vnet.ibm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, torvalds@linux-foundation.org, mark.rutland@arm.com, dhowells@redhat.com, linux-arch@vger.kernel.org, peterz@infradead.org, will.deacon@arm.com, "Paul E. McKenney" , Jonathan Corbet , Alexander Kuleshov Message-ID: <20171010002246.npV-_5ZQ4NTkbbx5TOdzW_za8koXmg1Pa7gvJ2EX2Wg@z> Now that smp_read_barrier_depends() is implied by READ_ONCE(), adding READ_ONCE() to assoc_array_ptr_to_leaf() and __assoc_array_ptr_to_meta() allows the several smp_read_barrier_depends() calls to be removed from lib/assoc_array.c. This commit makes this change. Signed-off-by: Paul E. McKenney Cc: Jonathan Corbet Cc: Mark Rutland Cc: Alexander Kuleshov --- include/linux/assoc_array_priv.h | 5 +++-- lib/assoc_array.c | 20 ++------------------ 2 files changed, 5 insertions(+), 20 deletions(-) diff --git a/include/linux/assoc_array_priv.h b/include/linux/assoc_array_priv.h index 711275e6681c..b47308bf1f99 100644 --- a/include/linux/assoc_array_priv.h +++ b/include/linux/assoc_array_priv.h @@ -135,13 +135,14 @@ static inline bool assoc_array_ptr_is_node(const struct assoc_array_ptr *x) static inline void *assoc_array_ptr_to_leaf(const struct assoc_array_ptr *x) { - return (void *)((unsigned long)x & ~ASSOC_ARRAY_PTR_TYPE_MASK); + return (void *)((unsigned long)READ_ONCE(x) & /* Address dependency. */ + ~ASSOC_ARRAY_PTR_TYPE_MASK); } static inline unsigned long __assoc_array_ptr_to_meta(const struct assoc_array_ptr *x) { - return (unsigned long)x & + return (unsigned long)READ_ONCE(x) & /* Address dependency. */ ~(ASSOC_ARRAY_PTR_SUBTYPE_MASK | ASSOC_ARRAY_PTR_TYPE_MASK); } static inline diff --git a/lib/assoc_array.c b/lib/assoc_array.c index fe7953aead82..52845f5cbf19 100644 --- a/lib/assoc_array.c +++ b/lib/assoc_array.c @@ -38,12 +38,10 @@ static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root, if (assoc_array_ptr_is_shortcut(cursor)) { /* Descend through a shortcut */ shortcut = assoc_array_ptr_to_shortcut(cursor); - smp_read_barrier_depends(); cursor = READ_ONCE(shortcut->next_node); } node = assoc_array_ptr_to_node(cursor); - smp_read_barrier_depends(); slot = 0; /* We perform two passes of each node. @@ -55,15 +53,9 @@ static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root, */ has_meta = 0; for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) { - ptr = READ_ONCE(node->slots[slot]); + ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */ has_meta |= (unsigned long)ptr; if (ptr && assoc_array_ptr_is_leaf(ptr)) { - /* We need a barrier between the read of the pointer - * and dereferencing the pointer - but only if we are - * actually going to dereference it. - */ - smp_read_barrier_depends(); - /* Invoke the callback */ ret = iterator(assoc_array_ptr_to_leaf(ptr), iterator_data); @@ -86,8 +78,6 @@ static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root, continue_node: node = assoc_array_ptr_to_node(cursor); - smp_read_barrier_depends(); - for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) { ptr = READ_ONCE(node->slots[slot]); if (assoc_array_ptr_is_meta(ptr)) { @@ -105,7 +95,6 @@ static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root, if (assoc_array_ptr_is_shortcut(parent)) { shortcut = assoc_array_ptr_to_shortcut(parent); - smp_read_barrier_depends(); cursor = parent; parent = READ_ONCE(shortcut->back_pointer); slot = shortcut->parent_slot; @@ -216,8 +205,6 @@ assoc_array_walk(const struct assoc_array *array, consider_node: node = assoc_array_ptr_to_node(cursor); - smp_read_barrier_depends(); - slot = segments >> (level & ASSOC_ARRAY_KEY_CHUNK_MASK); slot &= ASSOC_ARRAY_FAN_MASK; ptr = READ_ONCE(node->slots[slot]); @@ -254,7 +241,6 @@ assoc_array_walk(const struct assoc_array *array, cursor = ptr; follow_shortcut: shortcut = assoc_array_ptr_to_shortcut(cursor); - smp_read_barrier_depends(); pr_devel("shortcut to %d\n", shortcut->skip_to_level); sc_level = level + ASSOC_ARRAY_LEVEL_STEP; BUG_ON(sc_level > shortcut->skip_to_level); @@ -330,8 +316,7 @@ void *assoc_array_find(const struct assoc_array *array, assoc_array_walk_found_terminal_node) return NULL; - node = result.terminal_node.node; - smp_read_barrier_depends(); + node = READ_ONCE(result.terminal_node.node); /* Address dependency. */ /* If the target key is available to us, it's has to be pointed to by * the terminal node. @@ -344,7 +329,6 @@ void *assoc_array_find(const struct assoc_array *array, * actually going to dereference it. */ leaf = assoc_array_ptr_to_leaf(ptr); - smp_read_barrier_depends(); if (ops->compare_object(leaf, index_key)) return (void *)leaf; } -- 2.5.2