Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751809AbdCCQlu (ORCPT ); Fri, 3 Mar 2017 11:41:50 -0500 Received: from mx1.redhat.com ([209.132.183.28]:54118 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751310AbdCCQlr (ORCPT ); Fri, 3 Mar 2017 11:41:47 -0500 From: Vitaly Kuznetsov To: Dexuan Cui Cc: "gregkh\@linuxfoundation.org" , "Stephen Hemminger" , KY Srinivasan , Haiyang Zhang , "driverdev-devel\@linuxdriverproject.org" , "linux-kernel\@vger.kernel.org" Subject: Re: [PATCH] vmbus: remove hv_event_tasklet_disable/enable References: Date: Fri, 03 Mar 2017 17:40:47 +0100 In-Reply-To: (Dexuan Cui's message of "Thu, 2 Mar 2017 12:32:55 +0000") Message-ID: <874lzal3e8.fsf@vitty.brq.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Fri, 03 Mar 2017 16:40:50 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2842 Lines: 64 Dexuan Cui writes: > With the recent introduction of per-channel tasklet, we need to update > the way we handle the 3 concurrency issues: > > 1. hv_process_channel_removal -> percpu_channel_deq vs. > vmbus_chan_sched -> list_for_each_entry(..., percpu_list); > > 2. vmbus_process_offer -> percpu_channel_enq/deq vs. vmbus_chan_sched. > > 3. vmbus_close_internal vs. the per-channel tasklet vmbus_on_event; > > The first 2 issues can be handled by Stephen's recent patch > "vmbus: use rcu for per-cpu channel list", and the third issue > can be handled by calling tasklet_disable in vmbus_close_internal here. > > We don't need the original hv_event_tasklet_disable/enable since we > now use per-channel tasklet instead of the previous per-CPU tasklet, > and actually we must remove them due to the side effect now: > vmbus_process_offer -> hv_event_tasklet_enable -> tasklet_schedule will > start the per-channel callback prematurely, cauing NULL dereferencing > (the channel may haven't been properly configured to run the callback yet). > > Fixes: 631e63a9f346 ("vmbus: change to per channel tasklet") > > Signed-off-by: Dexuan Cui > Cc: "K. Y. Srinivasan" > Cc: Haiyang Zhang > Cc: Stephen Hemminger Tested-by: Vitaly Kuznetsov This patch fixes the following crash on boot: [ 1.451648] BUG: unable to handle kernel NULL pointer dereference at 0000000000000004 [ 1.452255] IP: netvsc_channel_cb+0x90/0x7b0 [hv_netvsc] [ 1.452255] PGD 0 [ 1.452255] [ 1.452255] Oops: 0000 [#1] SMP [ 1.452255] Modules linked in: hv_storvsc hv_netvsc(+) scsi_transport_fc hyperv_fb hyperv_keyboard hid_hyperv hv_vmbus [ 1.452255] CPU: 1 PID: 19 Comm: ksoftirqd/1 Not tainted 4.10.0_test+ #911 [ 1.452255] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v1.0 11/26/2012 [ 1.452255] task: ffff880007fd2b00 task.stack: ffffc90000e34000 [ 1.452255] RIP: 0010:netvsc_channel_cb+0x90/0x7b0 [hv_netvsc] ... [ 1.452255] Call Trace: [ 1.452255] vmbus_on_event+0x22/0x90 [hv_vmbus] [ 1.452255] tasklet_action+0x5e/0x110 [ 1.452255] __do_softirq+0x104/0x2af [ 1.452255] run_ksoftirqd+0x29/0x40 ... [ 1.548068] RIP: netvsc_channel_cb+0x90/0x7b0 [hv_netvsc] RSP: ffffc90000e37d88 [ 1.548068] CR2: 0000000000000004 [ 1.548068] ---[ end trace 601fd9d6588b21e5 ]--- [ 1.548068] Kernel panic - not syncing: Fatal exception in interrupt [ 1.548068] Kernel Offset: disabled [ 1.548068] ---[ end Kernel panic - not syncing: Fatal exception in interrupt [ 1.572155] ------------[ cut here ]------------ The crash is not imminent but it happens pretty often on boot, I think we need to push it to 4.11. -- Vitaly