From nobody Wed Nov 5 20:18:40 2025 Delivered-To: importer@patchew.org Received-SPF: temperror (zoho.com: Error in retrieving data from DNS) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=temperror (zoho.com: Error in retrieving data from DNS) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1536772406475324.4895521690944; Wed, 12 Sep 2018 10:13:26 -0700 (PDT) Received: from localhost ([::1]:37336 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1g08hh-0005wo-6K for importer@patchew.org; Wed, 12 Sep 2018 13:13:25 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33502) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1g08fF-0004Rr-DN for qemu-devel@nongnu.org; Wed, 12 Sep 2018 13:10:54 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1g08fE-0006pX-BQ for qemu-devel@nongnu.org; Wed, 12 Sep 2018 13:10:53 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:35446 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1g08fC-0006nv-67; Wed, 12 Sep 2018 13:10:50 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C9861804B9F4; Wed, 12 Sep 2018 17:10:49 +0000 (UTC) Received: from donizetti.redhat.com (unknown [10.36.118.61]) by smtp.corp.redhat.com (Postfix) with ESMTP id E1F2FA9A06; Wed, 12 Sep 2018 17:10:47 +0000 (UTC) From: Paolo Bonzini To: qemu-devel@nongnu.org Date: Wed, 12 Sep 2018 19:10:38 +0200 Message-Id: <20180912171040.1732-2-pbonzini@redhat.com> In-Reply-To: <20180912171040.1732-1-pbonzini@redhat.com> References: <20180912171040.1732-1-pbonzini@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Wed, 12 Sep 2018 17:10:49 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Wed, 12 Sep 2018 17:10:49 +0000 (UTC) for IP:'10.11.54.5' DOMAIN:'int-mx05.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'pbonzini@redhat.com' RCPT:'' X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 66.187.233.73 Subject: [Qemu-devel] [PATCH 1/3] aio-posix: fix concurrent access to poll_disable_cnt X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, famz@redhat.com, stefanha@redhat.com, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RDMRC_1 RSF_6 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" It is valid for an aio_set_fd_handler to happen concurrently with aio_poll. In that case, poll_disable_cnt can change under the heels of aio_poll, and the assertion on poll_disable_cnt can fail in run_poll_handlers. Therefore, this patch simply checks the counter on every polling iteration. There are no particular needs for ordering, since the polling loop is terminated anyway by aio_notify at the end of aio_set_fd_handler. Signed-off-by: Paolo Bonzini Reviewed-by: Fam Zheng --- util/aio-posix.c | 26 +++++++++++++++----------- 1 file changed, 15 insertions(+), 11 deletions(-) diff --git a/util/aio-posix.c b/util/aio-posix.c index 131ba6b4a8..5c29380575 100644 --- a/util/aio-posix.c +++ b/util/aio-posix.c @@ -211,6 +211,7 @@ void aio_set_fd_handler(AioContext *ctx, AioHandler *node; bool is_new =3D false; bool deleted =3D false; + int poll_disable_change; =20 qemu_lockcnt_lock(&ctx->list_lock); =20 @@ -244,11 +245,9 @@ void aio_set_fd_handler(AioContext *ctx, QLIST_REMOVE(node, node); deleted =3D true; } - - if (!node->io_poll) { - ctx->poll_disable_cnt--; - } + poll_disable_change =3D -!node->io_poll; } else { + poll_disable_change =3D !io_poll - (node && !node->io_poll); if (node =3D=3D NULL) { /* Alloc and insert if it's not already there */ node =3D g_new0(AioHandler, 1); @@ -257,10 +256,6 @@ void aio_set_fd_handler(AioContext *ctx, =20 g_source_add_poll(&ctx->source, &node->pfd); is_new =3D true; - - ctx->poll_disable_cnt +=3D !io_poll; - } else { - ctx->poll_disable_cnt +=3D !io_poll - !node->io_poll; } =20 /* Update handler with latest information */ @@ -274,6 +269,15 @@ void aio_set_fd_handler(AioContext *ctx, node->pfd.events |=3D (io_write ? G_IO_OUT | G_IO_ERR : 0); } =20 + /* No need to order poll_disable_cnt writes against other updates; + * the counter is only used to avoid wasting time and latency on + * iterated polling when the system call will be ultimately necessary. + * Changing handlers is a rare event, and a little wasted polling until + * the aio_notify below is not an issue. + */ + atomic_set(&ctx->poll_disable_cnt, + atomic_read(&ctx->poll_disable_cnt) + poll_disable_change); + aio_epoll_update(ctx, node, is_new); qemu_lockcnt_unlock(&ctx->list_lock); aio_notify(ctx); @@ -525,7 +529,6 @@ static bool run_poll_handlers(AioContext *ctx, int64_t = max_ns) =20 assert(ctx->notify_me); assert(qemu_lockcnt_count(&ctx->list_lock) > 0); - assert(ctx->poll_disable_cnt =3D=3D 0); =20 trace_run_poll_handlers_begin(ctx, max_ns); =20 @@ -533,7 +536,8 @@ static bool run_poll_handlers(AioContext *ctx, int64_t = max_ns) =20 do { progress =3D run_poll_handlers_once(ctx); - } while (!progress && qemu_clock_get_ns(QEMU_CLOCK_REALTIME) < end_tim= e); + } while (!progress && qemu_clock_get_ns(QEMU_CLOCK_REALTIME) < end_time + && !atomic_read(&ctx->poll_disable_cnt)); =20 trace_run_poll_handlers_end(ctx, progress); =20 @@ -552,7 +556,7 @@ static bool run_poll_handlers(AioContext *ctx, int64_t = max_ns) */ static bool try_poll_mode(AioContext *ctx, bool blocking) { - if (blocking && ctx->poll_max_ns && ctx->poll_disable_cnt =3D=3D 0) { + if (blocking && ctx->poll_max_ns && !atomic_read(&ctx->poll_disable_cn= t)) { /* See qemu_soonest_timeout() uint64_t hack */ int64_t max_ns =3D MIN((uint64_t)aio_compute_timeout(ctx), (uint64_t)ctx->poll_ns); --=20 2.17.1