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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 97AB0C5B543 for ; Fri, 30 May 2025 15:15:33 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uL1PL-0003lx-1X; Fri, 30 May 2025 11:12:31 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uL1PB-0003LB-Pg; Fri, 30 May 2025 11:12:22 -0400 Received: from proxmox-new.maurer-it.com ([94.136.29.106]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uL1P8-0002Hx-R2; Fri, 30 May 2025 11:12:21 -0400 Received: from proxmox-new.maurer-it.com (localhost.localdomain [127.0.0.1]) by proxmox-new.maurer-it.com (Proxmox) with ESMTP id 82CD144B56; Fri, 30 May 2025 17:11:46 +0200 (CEST) From: Fiona Ebner To: qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, kwolf@redhat.com, den@virtuozzo.com, andrey.drobyshev@virtuozzo.com, hreitz@redhat.com, stefanha@redhat.com, eblake@redhat.com, jsnow@redhat.com, vsementsov@yandex-team.ru, xiechanglong.d@gmail.com, wencongyang2@huawei.com, berto@igalia.com, fam@euphon.net, ari@tuxera.com Subject: [PATCH v4 23/48] block: never use atomics to access bs->quiesce_counter Date: Fri, 30 May 2025 17:11:00 +0200 Message-Id: <20250530151125.955508-24-f.ebner@proxmox.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250530151125.955508-1-f.ebner@proxmox.com> References: <20250530151125.955508-1-f.ebner@proxmox.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=94.136.29.106; envelope-from=f.ebner@proxmox.com; helo=proxmox-new.maurer-it.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org All accesses of bs->quiesce_counter are in the main thread, either after a GLOBAL_STATE_CODE() macro or in a function with GRAPH_WRLOCK annotation. This is essentially a revert of 414c2ec358 ("block: access quiesce_counter with atomic ops"). At that time, neither the GLOBAL_STATE_CODE() macro nor the GRAPH_WRLOCK annotation existed. Even if the field was only accessed in the main thread back then (did not check if that is actually the case), it wouldn't have been easy to verify. Signed-off-by: Fiona Ebner --- block/io.c | 7 ++----- include/block/block_int-common.h | 2 +- 2 files changed, 3 insertions(+), 6 deletions(-) diff --git a/block/io.c b/block/io.c index ac5c7174f6..9bd8ba8431 100644 --- a/block/io.c +++ b/block/io.c @@ -361,7 +361,7 @@ static void bdrv_do_drained_begin(BlockDriverState *bs, BdrvChild *parent, GLOBAL_STATE_CODE(); /* Stop things in parent-to-child order */ - if (qatomic_fetch_inc(&bs->quiesce_counter) == 0) { + if (bs->quiesce_counter++ == 0) { GRAPH_RDLOCK_GUARD_MAINLOOP(); bdrv_parent_drained_begin(bs, parent); if (bs->drv && bs->drv->bdrv_drain_begin) { @@ -401,8 +401,6 @@ bdrv_drained_begin(BlockDriverState *bs) */ static void bdrv_do_drained_end(BlockDriverState *bs, BdrvChild *parent) { - int old_quiesce_counter; - IO_OR_GS_CODE(); if (qemu_in_coroutine()) { @@ -415,8 +413,7 @@ static void bdrv_do_drained_end(BlockDriverState *bs, BdrvChild *parent) assert(bs->quiesce_counter > 0); /* Re-enable things in child-to-parent order */ - old_quiesce_counter = qatomic_fetch_dec(&bs->quiesce_counter); - if (old_quiesce_counter == 1) { + if (--bs->quiesce_counter == 0) { GRAPH_RDLOCK_GUARD_MAINLOOP(); if (bs->drv && bs->drv->bdrv_drain_end) { bs->drv->bdrv_drain_end(bs); diff --git a/include/block/block_int-common.h b/include/block/block_int-common.h index 925a3e7353..e96c6a6a03 100644 --- a/include/block/block_int-common.h +++ b/include/block/block_int-common.h @@ -1253,7 +1253,7 @@ struct BlockDriverState { /* do we need to tell the quest if we have a volatile write cache? */ int enable_write_cache; - /* Accessed with atomic ops. */ + /* Accessed only in the main thread. */ int quiesce_counter; unsigned int write_gen; /* Current data generation */ -- 2.39.5