From nobody Sun Nov 9 14:49:24 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) 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 [209.51.188.17]) by mx.zohomail.com with SMTPS id 155068055498927.69978787611933; Wed, 20 Feb 2019 08:35:54 -0800 (PST) Received: from localhost ([127.0.0.1]:42406 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gwUqc-0002mC-QH for importer@patchew.org; Wed, 20 Feb 2019 11:35:50 -0500 Received: from eggs.gnu.org ([209.51.188.92]:41504) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gwUOj-0002aZ-8r for qemu-devel@nongnu.org; Wed, 20 Feb 2019 11:07:03 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gwUOf-0005PP-Bw for qemu-devel@nongnu.org; Wed, 20 Feb 2019 11:07:01 -0500 Received: from mx1.redhat.com ([209.132.183.28]:57316) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gwUON-0005IT-SF for qemu-devel@nongnu.org; Wed, 20 Feb 2019 11:06:44 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1AF82B9A71 for ; Wed, 20 Feb 2019 16:06:37 +0000 (UTC) Received: from localhost (ovpn-112-64.ams2.redhat.com [10.36.112.64]) by smtp.corp.redhat.com (Postfix) with ESMTP id 656513792; Wed, 20 Feb 2019 16:06:36 +0000 (UTC) From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= To: qemu-devel@nongnu.org Date: Wed, 20 Feb 2019 17:06:26 +0100 Message-Id: <20190220160628.6555-3-marcandre.lureau@redhat.com> In-Reply-To: <20190220160628.6555-1-marcandre.lureau@redhat.com> References: <20190220160628.6555-1-marcandre.lureau@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Wed, 20 Feb 2019 16:06:37 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH 2/4] chardev: make qemu_chr_fe_set_handlers() context switching safer 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: Paolo Bonzini , Markus Armbruster , "Dr. David Alan Gilbert" , =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Type: text/plain; charset="utf-8" qemu_chr_fe_set_handlers() may switch the context of various sources. In order to prevent dispatch races from different threads, let's acquire or freeze the context, do all the source switches, and then release/resume the contexts. This should help to make context switching safer. Signed-off-by: Marc-Andr=C3=A9 Lureau --- include/chardev/char-fe.h | 23 +++++++++ chardev/char-fe.c | 103 +++++++++++++++++++++++++++++++++----- chardev/char-mux.c | 14 +++--- 3 files changed, 121 insertions(+), 19 deletions(-) diff --git a/include/chardev/char-fe.h b/include/chardev/char-fe.h index aa1b864ccd..4051435a1c 100644 --- a/include/chardev/char-fe.h +++ b/include/chardev/char-fe.h @@ -84,6 +84,14 @@ bool qemu_chr_fe_backend_open(CharBackend *be); * Set the front end char handlers. The front end takes the focus if * any of the handler is non-NULL. * + * A chardev may have multiple main loop sources. In order to prevent + * races when switching contexts, the function will temporarily block + * the contexts before the source switch to prevent them from + * dispatching in different threads concurrently. + * + * The current and the new @context must be acquirable or + * running & dispatched in a loop (the function will hang otherwise). + * * Without associated Chardev, nothing is changed. */ void qemu_chr_fe_set_handlers_full(CharBackend *b, @@ -110,6 +118,21 @@ void qemu_chr_fe_set_handlers(CharBackend *b, GMainContext *context, bool set_open); =20 +/** + * qemu_chr_fe_set_handlers_internal: + * + * Same as qemu_chr_fe_set_handlers(), without context freezing. + */ +void qemu_chr_fe_set_handlers_internal(CharBackend *b, + IOCanReadHandler *fd_can_read, + IOReadHandler *fd_read, + IOEventHandler *fd_event, + BackendChangeHandler *be_change, + void *opaque, + GMainContext *context, + bool set_open, + bool sync_state); + /** * qemu_chr_fe_take_focus: * diff --git a/chardev/char-fe.c b/chardev/char-fe.c index f3530a90e6..90cd7db007 100644 --- a/chardev/char-fe.c +++ b/chardev/char-fe.c @@ -246,15 +246,67 @@ void qemu_chr_fe_deinit(CharBackend *b, bool del) } } =20 -void qemu_chr_fe_set_handlers_full(CharBackend *b, - IOCanReadHandler *fd_can_read, - IOReadHandler *fd_read, - IOEventHandler *fd_event, - BackendChangeHandler *be_change, - void *opaque, - GMainContext *context, - bool set_open, - bool sync_state) +struct MainContextWait { + QemuCond cond; + QemuMutex lock; +}; + +static gboolean +main_context_wait_cb(gpointer user_data) +{ + struct MainContextWait *w =3D user_data; + + qemu_mutex_lock(&w->lock); + qemu_cond_signal(&w->cond); + /* wait until switching is over */ + qemu_cond_wait(&w->cond, &w->lock); + qemu_mutex_unlock(&w->lock); + + qemu_mutex_destroy(&w->lock); + qemu_cond_destroy(&w->cond); + g_free(w); + + return G_SOURCE_REMOVE; +} + +static void +main_context_wait(struct MainContextWait **wait, GMainContext *ctxt) +{ + struct MainContextWait *w =3D NULL; + + if (!g_main_context_acquire(ctxt)) { + w =3D g_new0(struct MainContextWait, 1); + qemu_mutex_init(&w->lock); + qemu_cond_init(&w->cond); + qemu_mutex_lock(&w->lock); + g_main_context_invoke(ctxt, main_context_wait_cb, w); + /* wait for the context to freeze */ + qemu_cond_wait(&w->cond, &w->lock); + qemu_mutex_unlock(&w->lock); + } + + *wait =3D w; +} + +static void +main_context_resume(struct MainContextWait *wait, GMainContext *ctxt) +{ + if (wait) { + qemu_cond_signal(&wait->cond); + } else { + g_main_context_release(ctxt); + } +} + +void qemu_chr_fe_set_handlers_internal(CharBackend *b, + IOCanReadHandler *fd_can_read, + IOReadHandler *fd_read, + IOEventHandler *fd_event, + BackendChangeHandler *be_change, + void *opaque, + GMainContext *new_context, + bool set_open, + bool sync_state) { Chardev *s; int fe_open; @@ -276,7 +328,7 @@ void qemu_chr_fe_set_handlers_full(CharBackend *b, b->chr_be_change =3D be_change; b->opaque =3D opaque; =20 - qemu_chr_be_update_read_handlers(s, context); + qemu_chr_be_update_read_handlers(s, new_context); =20 if (set_open) { qemu_chr_fe_set_open(b, fe_open); @@ -292,6 +344,34 @@ void qemu_chr_fe_set_handlers_full(CharBackend *b, } } =20 +void qemu_chr_fe_set_handlers_full(CharBackend *b, + IOCanReadHandler *fd_can_read, + IOReadHandler *fd_read, + IOEventHandler *fd_event, + BackendChangeHandler *be_change, + void *opaque, + GMainContext *new_context, + bool set_open, + bool sync_state) +{ + GMainContext *old_context =3D b->chr->gcontext; + struct MainContextWait *old_ctxt_wait, *new_ctxt_wait; + + main_context_wait(&old_ctxt_wait, old_context); + if (old_context !=3D new_context) { + main_context_wait(&new_ctxt_wait, new_context); + } + + qemu_chr_fe_set_handlers_internal(b, fd_can_read, fd_read, fd_event, + be_change, opaque, new_context, + set_open, sync_state); + + main_context_resume(old_ctxt_wait, old_context); + if (old_context !=3D new_context) { + main_context_resume(new_ctxt_wait, new_context); + } +} + void qemu_chr_fe_set_handlers(CharBackend *b, IOCanReadHandler *fd_can_read, IOReadHandler *fd_read, @@ -302,8 +382,7 @@ void qemu_chr_fe_set_handlers(CharBackend *b, bool set_open) { qemu_chr_fe_set_handlers_full(b, fd_can_read, fd_read, fd_event, be_ch= ange, - opaque, context, set_open, - true); + opaque, context, set_open, true); } =20 void qemu_chr_fe_take_focus(CharBackend *b) diff --git a/chardev/char-mux.c b/chardev/char-mux.c index 23aa82125d..9830cc4b37 100644 --- a/chardev/char-mux.c +++ b/chardev/char-mux.c @@ -283,13 +283,13 @@ static void mux_chr_update_read_handlers(Chardev *chr) MuxChardev *d =3D MUX_CHARDEV(chr); =20 /* Fix up the real driver with mux routines */ - qemu_chr_fe_set_handlers_full(&d->chr, - mux_chr_can_read, - mux_chr_read, - mux_chr_event, - NULL, - chr, - chr->gcontext, true, false); + qemu_chr_fe_set_handlers_internal(&d->chr, + mux_chr_can_read, + mux_chr_read, + mux_chr_event, + NULL, + chr, + chr->gcontext, true, false); } =20 void mux_set_focus(Chardev *chr, int focus) --=20 2.21.0.rc1