From patchwork Mon Mar 18 18:23:28 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= X-Patchwork-Id: 13595707 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 45541C54E5D for ; Mon, 18 Mar 2024 18:25:27 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rmHeP-0002DZ-9A; Mon, 18 Mar 2024 14:23:57 -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 1rmHeF-0002CD-22 for qemu-devel@nongnu.org; Mon, 18 Mar 2024 14:23:47 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rmHe9-0003jH-EY for qemu-devel@nongnu.org; Mon, 18 Mar 2024 14:23:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1710786220; h=from:from:reply-to:subject:subject: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=JPwNfk50/41cYcrfUvdjPncJaS8ETLis6wC+xOQh2/E=; b=f5XgKD3xSPr841by+ap97nnFyJLlyGAenOiHnVXtoQSeyd1PU8VLy78VjasBtvUi2WpEZC Oy01qj1IYSVvY7+wqY7R3jobRwSd4mCndQJDdOIJw/vJeR71g41r+0lVN6h2IJcYbiVhDJ 65XjL/bxdHAJnxLP9+CXde56XciTk2k= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-13-aiGnHB79P7W3Bqp5t6Wrrw-1; Mon, 18 Mar 2024 14:23:38 -0400 X-MC-Unique: aiGnHB79P7W3Bqp5t6Wrrw-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4896C84AEC8 for ; Mon, 18 Mar 2024 18:23:38 +0000 (UTC) Received: from toolbox.redhat.com (unknown [10.42.28.59]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2DE2C17A90; Mon, 18 Mar 2024 18:23:37 +0000 (UTC) From: =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= To: qemu-devel@nongnu.org Cc: Paolo Bonzini , Thomas Huth , =?utf-8?q?Marc-Andr=C3=A9_Lureau?= , =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= Subject: [PATCH 1/3 for 9.0] chardev: lower priority of the HUP GSource in socket chardev Date: Mon, 18 Mar 2024 18:23:28 +0000 Message-ID: <20240318182330.96738-2-berrange@redhat.com> In-Reply-To: <20240318182330.96738-1-berrange@redhat.com> References: <20240318182330.96738-1-berrange@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.5 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.374, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 The socket chardev often has 2 GSource object registered against the same FD. One is registered all the time and is just intended to handle POLLHUP events, while the other gets registered & unregistered on the fly as the frontend is ready to receive more data or not. It is very common for poll() to signal a POLLHUP event at the same time as there is pending incoming data from the disconnected client. It is therefore essential to process incoming data prior to processing HUP. The problem with having 2 GSource on the same FD is that there is no guaranteed ordering of execution between them, so the chardev code may process HUP first and thus discard data. This failure scenario is non-deterministic but can be seen fairly reliably by reverting a7077b8e354d90fec26c2921aa2dea85b90dff90, and then running 'tests/unit/test-char', which will sometimes fail with missing data. Ideally QEMU would only have 1 GSource, but that's a complex code refactoring job. The next best solution is to try to ensure ordering between the 2 GSource objects. This can be achieved by lowering the priority of the HUP GSource, so that it is never dispatched if the main GSource is also ready to dispatch. Counter-intuitively, lowering the priority of a GSource is done by raising its priority number. Signed-off-by: Daniel P. Berrangé Reviewed-by: Marc-André Lureau Reviewed-by: Thomas Huth --- chardev/char-socket.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/chardev/char-socket.c b/chardev/char-socket.c index 8a0406cc1e..2c4dffc0e6 100644 --- a/chardev/char-socket.c +++ b/chardev/char-socket.c @@ -601,6 +601,22 @@ static void update_ioc_handlers(SocketChardev *s) remove_hup_source(s); s->hup_source = qio_channel_create_watch(s->ioc, G_IO_HUP); + /* + * poll() is liable to return POLLHUP even when there is + * still incoming data available to read on the FD. If + * we have the hup_source at the same priority as the + * main io_add_watch_poll GSource, then we might end up + * processing the POLLHUP event first, closing the FD, + * and as a result silently discard data we should have + * read. + * + * By setting the hup_source to G_PRIORITY_DEFAULT + 1, + * we ensure that io_add_watch_poll GSource will always + * be dispatched first, thus guaranteeing we will be + * able to process all incoming data before closing the + * FD + */ + g_source_set_priority(s->hup_source, G_PRIORITY_DEFAULT + 1); g_source_set_callback(s->hup_source, (GSourceFunc)tcp_chr_hup, chr, NULL); g_source_attach(s->hup_source, chr->gcontext); From patchwork Mon Mar 18 18:23:29 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= X-Patchwork-Id: 13595704 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 AFB76C54E58 for ; Mon, 18 Mar 2024 18:24:49 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rmHeK-0002DP-UU; Mon, 18 Mar 2024 14:23:52 -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 1rmHeH-0002Cx-Vi for qemu-devel@nongnu.org; Mon, 18 Mar 2024 14:23:50 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rmHeB-0003jS-SY for qemu-devel@nongnu.org; Mon, 18 Mar 2024 14:23:49 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1710786222; h=from:from:reply-to:subject:subject: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=qWv0N87mex1mgDV6ALULC06NKBETKhw3uvoJ4y4Jqkg=; b=UEuefUka0y+cY6vrjcyEdSy02TrshyAKS18R/dXl1gVOlEZ34rgCvUQZAPeEVb6CwlM3ci zmKgk0tn8ZQcLNY5wLrWgEpFmFFlKepWAEfa8AsTZ8L9NgIu/9QIEve0tYfgXGDDmEQZl4 LFf6tZVx7o6rey41Ppj28vfvpjHkawE= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-232-CAXZNPMfOzad0pp12XJ0Fw-1; Mon, 18 Mar 2024 14:23:40 -0400 X-MC-Unique: CAXZNPMfOzad0pp12XJ0Fw-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 291A81869D0C for ; Mon, 18 Mar 2024 18:23:40 +0000 (UTC) Received: from toolbox.redhat.com (unknown [10.42.28.59]) by smtp.corp.redhat.com (Postfix) with ESMTP id 956DF17AAF; Mon, 18 Mar 2024 18:23:38 +0000 (UTC) From: =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= To: qemu-devel@nongnu.org Cc: Paolo Bonzini , Thomas Huth , =?utf-8?q?Marc-Andr=C3=A9_Lureau?= , =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= Subject: [PATCH 2/3 for 9.0] Revert "chardev/char-socket: Fix TLS io channels sending too much data to the backend" Date: Mon, 18 Mar 2024 18:23:29 +0000 Message-ID: <20240318182330.96738-3-berrange@redhat.com> In-Reply-To: <20240318182330.96738-1-berrange@redhat.com> References: <20240318182330.96738-1-berrange@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.5 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.374, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 This commit results in unexpected termination of the TLS connection. When 'fd_can_read' returns 0, the code goes on to pass a zero length buffer to qio_channel_read. The TLS impl calls into gnutls_recv() with this zero length buffer, at which point GNUTLS returns an error GNUTLS_E_INVALID_REQUEST. This is treated as fatal by QEMU's TLS code resulting in the connection being torn down by the chardev. Simply skipping the qio_channel_read when the buffer length is zero is also not satisfactory, as it results in a high CPU burn busy loop massively slowing QEMU's functionality. The proper solution is to avoid tcp_chr_read being called at all unless the frontend is able to accept more data. This will be done in a followup commit. This reverts commit 1907f4d149c3589ade641423c6a33fd7598fa4d3. Signed-off-by: Daniel P. Berrangé Reviewed-by: Thomas Huth --- chardev/char-socket.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/chardev/char-socket.c b/chardev/char-socket.c index 2c4dffc0e6..812d7aa38a 100644 --- a/chardev/char-socket.c +++ b/chardev/char-socket.c @@ -496,9 +496,9 @@ static gboolean tcp_chr_read(QIOChannel *chan, GIOCondition cond, void *opaque) s->max_size <= 0) { return TRUE; } - len = tcp_chr_read_poll(opaque); - if (len > sizeof(buf)) { - len = sizeof(buf); + len = sizeof(buf); + if (len > s->max_size) { + len = s->max_size; } size = tcp_chr_recv(chr, (void *)buf, len); if (size == 0 || (size == -1 && errno != EAGAIN)) { From patchwork Mon Mar 18 18:23:30 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= X-Patchwork-Id: 13595706 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 AC918C54E58 for ; Mon, 18 Mar 2024 18:25:10 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rmHeH-0002Ci-LF; Mon, 18 Mar 2024 14:23:49 -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 1rmHeF-0002CY-Oj for qemu-devel@nongnu.org; Mon, 18 Mar 2024 14:23:47 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rmHeD-0003jh-RX for qemu-devel@nongnu.org; Mon, 18 Mar 2024 14:23:47 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1710786224; h=from:from:reply-to:subject:subject: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=TdZ3kCB5zvIKEzBCdWrLUr1ksdmEF/TRdxxVtwG2b1A=; b=SJfNiOwpPvCkXKSqPqElBG+DtsW1fDeLRDh0mLmY5NaF0PT5SOHHzbceGvvUn/gf5hvN8+ QWRvZPIBnH7IGsHJV/TmcKCmnlNCz47n6JRGHvQfY3O62Bnf9JIUqDmgms8Yt8g/JGbtjM jHaJC1NjSY+BpKD782CcXSf1wl5reDE= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-230-Dj8xFvr_MyWltylOwaerww-1; Mon, 18 Mar 2024 14:23:42 -0400 X-MC-Unique: Dj8xFvr_MyWltylOwaerww-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C72C21013660 for ; Mon, 18 Mar 2024 18:23:41 +0000 (UTC) Received: from toolbox.redhat.com (unknown [10.42.28.59]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8A2C517A9A; Mon, 18 Mar 2024 18:23:40 +0000 (UTC) From: =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= To: qemu-devel@nongnu.org Cc: Paolo Bonzini , Thomas Huth , =?utf-8?q?Marc-Andr=C3=A9_Lureau?= , =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= Subject: [PATCH 3/3 for 9.0] Revert "chardev: use a child source for qio input source" Date: Mon, 18 Mar 2024 18:23:30 +0000 Message-ID: <20240318182330.96738-4-berrange@redhat.com> In-Reply-To: <20240318182330.96738-1-berrange@redhat.com> References: <20240318182330.96738-1-berrange@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.5 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.374, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 This reverts commit a7077b8e354d90fec26c2921aa2dea85b90dff90, and add comments to explain why child sources cannot be used. When a GSource is added as a child of another GSource, if its 'prepare' function indicates readiness, then the parent's 'prepare' function will never be run. The io_watch_poll_prepare absolutely *must* be run on every iteration of the main loop, to ensure that the chardev backend doesn't feed data to the frontend that it is unable to consume. At the time a7077b8e354d90fec26c2921aa2dea85b90dff90 was made, all the child GSource impls were relying on poll'ing an FD, so their 'prepare' functions would never indicate readiness ahead of poll() being invoked. So the buggy behaviour was not noticed and lay dormant. Relatively recently the QIOChannelTLS impl introduced a level 2 child GSource, which checks with GNUTLS whether it has cached any data that was decoded but not yet consumed: commit ffda5db65aef42266a5053a4be34515106c4c7ee Author: Antoine Damhet Date: Tue Nov 15 15:23:29 2022 +0100 io/channel-tls: fix handling of bigger read buffers Since the TLS backend can read more data from the underlying QIOChannel we introduce a minimal child GSource to notify if we still have more data available to be read. Signed-off-by: Antoine Damhet Signed-off-by: Charles Frey Signed-off-by: Daniel P. Berrangé With this, it is now quite common for the 'prepare' function on a QIOChannelTLS GSource to indicate immediate readiness, bypassing the parent GSource 'prepare' function. IOW, the critical 'io_watch_poll_prepare' is being skipped on some iterations of the main loop. As a result chardev frontend asserts are now being triggered as they are fed data they are not ready to consume. A reproducer is as follows: * In terminal 1 run a GNUTLS *echo* server $ gnutls-serv --echo \ --x509cafile ca-cert.pem \ --x509keyfile server-key.pem \ --x509certfile server-cert.pem \ -p 9000 * In terminal 2 run a QEMU guest $ qemu-system-s390x \ -nodefaults \ -display none \ -object tls-creds-x509,id=tls0,dir=$PWD,endpoint=client \ -chardev socket,id=con0,host=localhost,port=9000,tls-creds=tls0 \ -device sclpconsole,chardev=con0 \ -hda Fedora-Cloud-Base-39-1.5.s390x.qcow2 After the previous patch revert, but before this patch revert, this scenario will crash: qemu-system-s390x: ../hw/char/sclpconsole.c:73: chr_read: Assertion `size <= SIZE_BUFFER_VT220 - scon->iov_data_len' failed. This assert indicates that 'tcp_chr_read' was called without 'tcp_chr_read_poll' having first been checked for ability to receive more data QEMU's use of a 'prepare' function to create/delete another GSource is rather a hack and not normally the kind of thing that is expected to be done by a GSource. There is no mechanism to force GLib to always run the 'prepare' function of a parent GSource. The best option is to simply not use the child source concept, and go back to the functional approach previously relied on. Signed-off-by: Daniel P. Berrangé Reviewed-by: Marc-André Lureau Reviewed-by: Thomas Huth --- chardev/char-io.c | 55 ++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 50 insertions(+), 5 deletions(-) diff --git a/chardev/char-io.c b/chardev/char-io.c index 4451128cba..3c725f530b 100644 --- a/chardev/char-io.c +++ b/chardev/char-io.c @@ -33,6 +33,7 @@ typedef struct IOWatchPoll { IOCanReadHandler *fd_can_read; GSourceFunc fd_read; void *opaque; + GMainContext *context; } IOWatchPoll; static IOWatchPoll *io_watch_poll_from_source(GSource *source) @@ -50,28 +51,58 @@ static gboolean io_watch_poll_prepare(GSource *source, return FALSE; } + /* + * We do not register the QIOChannel watch as a child GSource. + * The 'prepare' function on the parent GSource will be + * skipped if a child GSource's 'prepare' function indicates + * readiness. We need this prepare function be guaranteed + * to run on *every* iteration of the main loop, because + * it is critical to ensure we remove the QIOChannel watch + * if 'fd_can_read' indicates the frontend cannot receive + * more data. + */ if (now_active) { iwp->src = qio_channel_create_watch( iwp->ioc, G_IO_IN | G_IO_ERR | G_IO_HUP | G_IO_NVAL); g_source_set_callback(iwp->src, iwp->fd_read, iwp->opaque, NULL); - g_source_add_child_source(source, iwp->src); - g_source_unref(iwp->src); + g_source_attach(iwp->src, iwp->context); } else { - g_source_remove_child_source(source, iwp->src); + g_source_destroy(iwp->src); + g_source_unref(iwp->src); iwp->src = NULL; } return FALSE; } +static gboolean io_watch_poll_check(GSource *source) +{ + return FALSE; +} + static gboolean io_watch_poll_dispatch(GSource *source, GSourceFunc callback, gpointer user_data) { - return G_SOURCE_CONTINUE; + abort(); +} + +static void io_watch_poll_finalize(GSource *source) +{ + /* Due to a glib bug, removing the last reference to a source + * inside a finalize callback causes recursive locking (and a + * deadlock). This is not a problem inside other callbacks, + * including dispatch callbacks, so we call io_remove_watch_poll + * to remove this source. At this point, iwp->src must + * be NULL, or we would leak it. + */ + IOWatchPoll *iwp = io_watch_poll_from_source(source); + assert(iwp->src == NULL); } static GSourceFuncs io_watch_poll_funcs = { .prepare = io_watch_poll_prepare, + .check = io_watch_poll_check, .dispatch = io_watch_poll_dispatch, + .finalize = io_watch_poll_finalize, }; GSource *io_add_watch_poll(Chardev *chr, @@ -91,6 +122,7 @@ GSource *io_add_watch_poll(Chardev *chr, iwp->ioc = ioc; iwp->fd_read = (GSourceFunc) fd_read; iwp->src = NULL; + iwp->context = context; name = g_strdup_printf("chardev-iowatch-%s", chr->label); g_source_set_name((GSource *)iwp, name); @@ -101,10 +133,23 @@ GSource *io_add_watch_poll(Chardev *chr, return (GSource *)iwp; } +static void io_remove_watch_poll(GSource *source) +{ + IOWatchPoll *iwp; + + iwp = io_watch_poll_from_source(source); + if (iwp->src) { + g_source_destroy(iwp->src); + g_source_unref(iwp->src); + iwp->src = NULL; + } + g_source_destroy(&iwp->parent); +} + void remove_fd_in_watch(Chardev *chr) { if (chr->gsource) { - g_source_destroy(chr->gsource); + io_remove_watch_poll(chr->gsource); chr->gsource = NULL; } }