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 X-Spam-Level: X-Spam-Status: No, score=-18.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_RED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 62D95C4332D for ; Mon, 28 Dec 2020 13:59:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 389C62064B for ; Mon, 28 Dec 2020 13:59:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2407928AbgL1N7m (ORCPT ); Mon, 28 Dec 2020 08:59:42 -0500 Received: from mail.kernel.org ([198.145.29.99]:33326 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2436505AbgL1N7d (ORCPT ); Mon, 28 Dec 2020 08:59:33 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 04295207BC; Mon, 28 Dec 2020 13:58:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1609163932; bh=yRp7TAlyMOY3UjlQS2qI9K6VQ2w8z6dQqYEKaquX9g0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Trdry1H27AwtGDmML/ooSGeVfybZcxyq2YuCAoqgyjyixCUeYaf1qJgAWqQ5whR8e YIkuFo6ug2LQ2WVDKDHSJhUZGHdZmKQaFeqtKn5u+KEigm+MCFFyo4qVkopcEw+x4O JDuJmjcmqPONnZUj3qwJ22FaaEeq5L/rq5zPJBA8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, SeongJae Park , Michael Kurth , Pawel Wieczorkiewicz , Juergen Gross Subject: [PATCH 5.4 443/453] xen/xenbus: Allow watches discard events before queueing Date: Mon, 28 Dec 2020 13:51:19 +0100 Message-Id: <20201228124958.537598224@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201228124937.240114599@linuxfoundation.org> References: <20201228124937.240114599@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: SeongJae Park commit fed1755b118147721f2c87b37b9d66e62c39b668 upstream. If handling logics of watch events are slower than the events enqueue logic and the events can be created from the guests, the guests could trigger memory pressure by intensively inducing the events, because it will create a huge number of pending events that exhausting the memory. Fortunately, some watch events could be ignored, depending on its handler callback. For example, if the callback has interest in only one single path, the watch wouldn't want multiple pending events. Or, some watches could ignore events to same path. To let such watches to volutarily help avoiding the memory pressure situation, this commit introduces new watch callback, 'will_handle'. If it is not NULL, it will be called for each new event just before enqueuing it. Then, if the callback returns false, the event will be discarded. No watch is using the callback for now, though. This is part of XSA-349 Cc: stable@vger.kernel.org Signed-off-by: SeongJae Park Reported-by: Michael Kurth Reported-by: Pawel Wieczorkiewicz Reviewed-by: Juergen Gross Signed-off-by: Juergen Gross Signed-off-by: Greg Kroah-Hartman --- drivers/net/xen-netback/xenbus.c | 4 ++++ drivers/xen/xenbus/xenbus_client.c | 1 + drivers/xen/xenbus/xenbus_xs.c | 5 ++++- include/xen/xenbus.h | 7 +++++++ 4 files changed, 16 insertions(+), 1 deletion(-) --- a/drivers/net/xen-netback/xenbus.c +++ b/drivers/net/xen-netback/xenbus.c @@ -713,12 +713,14 @@ static int xen_register_credit_watch(str return -ENOMEM; snprintf(node, maxlen, "%s/rate", dev->nodename); vif->credit_watch.node = node; + vif->credit_watch.will_handle = NULL; vif->credit_watch.callback = xen_net_rate_changed; err = register_xenbus_watch(&vif->credit_watch); if (err) { pr_err("Failed to set watcher %s\n", vif->credit_watch.node); kfree(node); vif->credit_watch.node = NULL; + vif->credit_watch.will_handle = NULL; vif->credit_watch.callback = NULL; } return err; @@ -765,6 +767,7 @@ static int xen_register_mcast_ctrl_watch snprintf(node, maxlen, "%s/request-multicast-control", dev->otherend); vif->mcast_ctrl_watch.node = node; + vif->mcast_ctrl_watch.will_handle = NULL; vif->mcast_ctrl_watch.callback = xen_mcast_ctrl_changed; err = register_xenbus_watch(&vif->mcast_ctrl_watch); if (err) { @@ -772,6 +775,7 @@ static int xen_register_mcast_ctrl_watch vif->mcast_ctrl_watch.node); kfree(node); vif->mcast_ctrl_watch.node = NULL; + vif->mcast_ctrl_watch.will_handle = NULL; vif->mcast_ctrl_watch.callback = NULL; } return err; --- a/drivers/xen/xenbus/xenbus_client.c +++ b/drivers/xen/xenbus/xenbus_client.c @@ -120,6 +120,7 @@ int xenbus_watch_path(struct xenbus_devi int err; watch->node = path; + watch->will_handle = NULL; watch->callback = callback; err = register_xenbus_watch(watch); --- a/drivers/xen/xenbus/xenbus_xs.c +++ b/drivers/xen/xenbus/xenbus_xs.c @@ -705,7 +705,10 @@ int xs_watch_msg(struct xs_watch_event * spin_lock(&watches_lock); event->handle = find_watch(event->token); - if (event->handle != NULL) { + if (event->handle != NULL && + (!event->handle->will_handle || + event->handle->will_handle(event->handle, + event->path, event->token))) { spin_lock(&watch_events_lock); list_add_tail(&event->list, &watch_events); wake_up(&watch_events_waitq); --- a/include/xen/xenbus.h +++ b/include/xen/xenbus.h @@ -59,6 +59,13 @@ struct xenbus_watch /* Path being watched. */ const char *node; + /* + * Called just before enqueing new event while a spinlock is held. + * The event will be discarded if this callback returns false. + */ + bool (*will_handle)(struct xenbus_watch *, + const char *path, const char *token); + /* Callback (executed in a process context with no locks held). */ void (*callback)(struct xenbus_watch *, const char *path, const char *token);