From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:51472 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726294AbeK0GaO (ORCPT ); Tue, 27 Nov 2018 01:30:14 -0500 Date: Mon, 26 Nov 2018 20:35:03 +0100 From: Greg KH To: kys@microsoft.com Cc: 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, Haiyang Zhang , stable@vger.kernel.org Subject: Re: [PATCH 2/2] Drivers: hv: vmbus: offload the handling of channels to two workqueues Message-ID: <20181126193503.GA25649@kroah.com> 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 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 > --- > drivers/hv/channel_mgmt.c | 188 +++++++++++++++++++++++++------------- > drivers/hv/connection.c | 24 ++++- > drivers/hv/hyperv_vmbus.h | 7 ++ > include/linux/hyperv.h | 7 ++ > 4 files changed, 161 insertions(+), 65 deletions(-) As Sasha pointed out, this patch does not even apply :(