From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756008AbdJJAZw (ORCPT ); Mon, 9 Oct 2017 20:25:52 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:48199 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755791AbdJJAWz (ORCPT ); Mon, 9 Oct 2017 20:22:55 -0400 From: "Paul E. McKenney" 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 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 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20171010001951.GA6476@linux.vnet.ibm.com> References: <20171010001951.GA6476@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17101000-0036-0000-0000-000002792E56 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007870; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000235; SDB=6.00928858; UDB=6.00467489; IPR=6.00709129; BA=6.00005631; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00017467; XFM=3.00000015; UTC=2017-10-10 00:22:53 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17101000-0037-0000-0000-00004206C52C Message-Id: <1507594969-8347-12-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-10-09_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=1 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1710100003 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@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