From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:59286 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726145AbeKZQQd (ORCPT ); Mon, 26 Nov 2018 11:16:33 -0500 Date: Mon, 26 Nov 2018 00:23:31 -0500 From: Sasha Levin To: kys@microsoft.com Cc: gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, devel@linuxdriverproject.org, olaf@aepfle.de, apw@canonical.com, jasowang@redhat.com, sthemmin@microsoft.com, Michael.H.Kelley@microsoft.com, vkuznets@redhat.com, Dexuan Cui , stable@vger.kernel.org, Haiyang Zhang Subject: Re: [PATCH 2/2] Drivers: hv: vmbus: offload the handling of channels to two workqueues Message-ID: <20181126052331.GA34679@sasha-vm> References: <20181126022821.11269-1-kys@linuxonhyperv.com> <20181126022958.11320-1-kys@linuxonhyperv.com> <20181126022958.11320-2-kys@linuxonhyperv.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20181126022958.11320-2-kys@linuxonhyperv.com> Sender: stable-owner@vger.kernel.org List-ID: On Mon, Nov 26, 2018 at 02:29:57AM +0000, kys@linuxonhyperv.com wrote: >From: Dexuan Cui > >vmbus_process_offer() mustn't call channel->sc_creation_callback() >directly for sub-channels, because sc_creation_callback() -> >vmbus_open() may never get the host's response to the >OPEN_CHANNEL message (the host may rescind a channel at any time, >e.g. in the case of hot removing a NIC), and vmbus_onoffer_rescind() >may not wake up the vmbus_open() as it's blocked due to a non-zero >vmbus_connection.offer_in_progress, and finally we have a deadlock. > >The above is also true for primary channels, if the related device >drivers use sync probing mode by default. > >And, usually the handling of primary channels and sub-channels can >depend on each other, so we should offload them to different >workqueues to avoid possible deadlock, e.g. in sync-probing mode, >NIC1's netvsc_subchan_work() can race with NIC2's netvsc_probe() -> >rtnl_lock(), and causes deadlock: the former gets the rtnl_lock >and waits for all the sub-channels to appear, but the latter >can't get the rtnl_lock and this blocks the handling of sub-channels. > >The patch can fix the multiple-NIC deadlock described above for >v3.x kernels (e.g. RHEL 7.x) which don't support async-probing >of devices, and v4.4, v4.9, v4.14 and v4.18 which support async-probing >but don't enable async-probing for Hyper-V drivers (yet). > >The patch can also fix the hang issue in sub-channel's handling described >above for all versions of kernels, including v4.19 and v4.20-rc3. > >So the patch should be applied to all the existing kernels. > >Fixes: 8195b1396ec8 ("hv_netvsc: fix deadlock on hotplug") >Cc: stable@vger.kernel.org >Cc: Stephen Hemminger >Cc: K. Y. Srinivasan >Cc: Haiyang Zhang >Signed-off-by: Dexuan Cui >Signed-off-by: K. Y. Srinivasan This patch doesn't apply on next/linus/char-misc; there seems to be a missing patch that touches vmbus_process_offer() which isn't a part of this series. -- Thanks, Sasha