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=-17.2 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_BLOCKED, USER_AGENT_SANE_1 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 191D2C2D0E4 for ; Mon, 23 Nov 2020 13:30:39 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 90143206E3 for ; Mon, 23 Nov 2020 13:30:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="BG9k2RjR" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 90143206E3 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.34300.65245 (Exim 4.92) (envelope-from ) id 1khBvI-0000HT-Tm; Mon, 23 Nov 2020 13:30:28 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 34300.65245; Mon, 23 Nov 2020 13:30:28 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1khBvI-0000HL-Qf; Mon, 23 Nov 2020 13:30:28 +0000 Received: by outflank-mailman (input) for mailman id 34300; Mon, 23 Nov 2020 13:30:28 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1khBvI-0000HE-0F for xen-devel@lists.xenproject.org; Mon, 23 Nov 2020 13:30:28 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 287d2545-a77c-426f-8d65-7c70bb0fa7d7; Mon, 23 Nov 2020 13:30:27 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 5CD23AF16; Mon, 23 Nov 2020 13:30:26 +0000 (UTC) Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1khBvI-0000HE-0F for xen-devel@lists.xenproject.org; Mon, 23 Nov 2020 13:30:28 +0000 X-Inumbo-ID: 287d2545-a77c-426f-8d65-7c70bb0fa7d7 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 287d2545-a77c-426f-8d65-7c70bb0fa7d7; Mon, 23 Nov 2020 13:30:27 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1606138226; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=7jt0BkRlKG8ZX6o9qxDhFaVFYDZdwpFBoupgoJURDZ8=; b=BG9k2RjRcZu8KM66M5gYSdqbg/ZJjaxOQBOZ1vp66TrSez4PyekKHZ4NKfM6EnVGUa1+kI 8wZSo+8viK66yeY0eBzxSnMbVbwtVlJSdKHbPWURRT0cARKTGaq8IomDc3aB64DgbG9hoH JEoVOivGheiKmUT1htOCisPPxKpxh4s= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 5CD23AF16; Mon, 23 Nov 2020 13:30:26 +0000 (UTC) Subject: [PATCH v3 5/5] evtchn: don't call Xen consumer callback with per-channel lock held From: Jan Beulich To: "xen-devel@lists.xenproject.org" Cc: Andrew Cooper , George Dunlap , Ian Jackson , Julien Grall , Wei Liu , Stefano Stabellini , Tamas K Lengyel , Petre Ovidiu PIRCALABU , Alexandru Isaila References: <9d7a052a-6222-80ff-cbf1-612d4ca50c2a@suse.com> Message-ID: Date: Mon, 23 Nov 2020 14:30:25 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <9d7a052a-6222-80ff-cbf1-612d4ca50c2a@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit While there don't look to be any problems with this right now, the lock order implications from holding the lock can be very difficult to follow (and may be easy to violate unknowingly). The present callbacks don't (and no such callback should) have any need for the lock to be held. However, vm_event_disable() frees the structures used by respective callbacks and isn't otherwise synchronized with invocations of these callbacks, so maintain a count of in-progress calls, for evtchn_close() to wait to drop to zero before freeing the port (and dropping the lock). Signed-off-by: Jan Beulich --- Should we make this accounting optional, to be requested through a new parameter to alloc_unbound_xen_event_channel(), or derived from other than the default callback being requested? --- v3: Drain callbacks before proceeding with closing. Re-base. --- a/xen/common/event_channel.c +++ b/xen/common/event_channel.c @@ -397,6 +397,7 @@ static long evtchn_bind_interdomain(evtc rchn->u.interdomain.remote_dom = ld; rchn->u.interdomain.remote_port = lport; + atomic_set(&rchn->u.interdomain.active_calls, 0); rchn->state = ECS_INTERDOMAIN; /* @@ -720,6 +721,10 @@ int evtchn_close(struct domain *d1, int double_evtchn_lock(chn1, chn2); + if ( consumer_is_xen(chn1) ) + while ( atomic_read(&chn1->u.interdomain.active_calls) ) + cpu_relax(); + evtchn_free(d1, chn1); chn2->state = ECS_UNBOUND; @@ -781,9 +786,15 @@ int evtchn_send(struct domain *ld, unsig rport = lchn->u.interdomain.remote_port; rchn = evtchn_from_port(rd, rport); if ( consumer_is_xen(rchn) ) + { + /* Don't keep holding the lock for the call below. */ + atomic_inc(&rchn->u.interdomain.active_calls); + evtchn_read_unlock(lchn); xen_notification_fn(rchn)(rd->vcpu[rchn->notify_vcpu_id], rport); - else - evtchn_port_set_pending(rd, rchn->notify_vcpu_id, rchn); + atomic_dec(&rchn->u.interdomain.active_calls); + return 0; + } + evtchn_port_set_pending(rd, rchn->notify_vcpu_id, rchn); break; case ECS_IPI: evtchn_port_set_pending(ld, lchn->notify_vcpu_id, lchn); --- a/xen/include/xen/sched.h +++ b/xen/include/xen/sched.h @@ -104,6 +104,7 @@ struct evtchn } unbound; /* state == ECS_UNBOUND */ struct { evtchn_port_t remote_port; + atomic_t active_calls; struct domain *remote_dom; } interdomain; /* state == ECS_INTERDOMAIN */ struct {