Return-path: Received: from smtp.codeaurora.org ([198.145.29.96]:33700 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753701AbdBHKrG (ORCPT ); Wed, 8 Feb 2017 05:47:06 -0500 From: Kalle Valo To: Paolo Abeni Cc: Arend Van Spriel , linux-wireless@vger.kernel.org, brcm80211-dev-list.pdl@broadcom.com, Franky Lin , hante Meuleman Subject: Re: [PATCH net] brcmfmac: clear skb head state on xmit References: <1486543119.2533.3.camel@redhat.com> Date: Wed, 08 Feb 2017 12:27:42 +0200 In-Reply-To: <1486543119.2533.3.camel@redhat.com> (Paolo Abeni's message of "Wed, 08 Feb 2017 09:38:39 +0100") Message-ID: <87zihxm0yp.fsf@kamboji.qca.qualcomm.com> (sfid-20170208_115114_089628_C54BB1ED) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-wireless-owner@vger.kernel.org List-ID: Paolo Abeni writes: > On Tue, 2017-02-07 at 20:23 +0100, Arend Van Spriel wrote: >> On 7-2-2017 17:50, Paolo Abeni wrote: >> > the skbs can be held by the driver for a long time, so we need >> > to clear any state on xmit to avoid hanging other subsystems. >> > The skbs are already orphaned later in cmsg code, so we just >> > need to clear the nf/dst/secpath. >> > Do it early, while the relevant entries are hopefully still >> > hot in the cache. >> >> What is this about really? A bit more background about the issue >> might >> help understanding the need for this patch. Is this really specific >> to >> brcmfmac. For instance is something similar already done in mac80211? > > The issue is apparently driver specific, as reported in: > > https://bugzilla.redhat.com/show_bug.cgi?id=1294415 > > This is caused by xmit skbs carrying a notrack ct entry not being freed > by the device driver in a timely manner. Removing the ct module waits > for such entries refcount going to zero and hangs the kernel in busy > loop (for several minutes). > > The relevant skbs are icmp6 packets (ND if I recall correctly, they > bcast packets at the mac level). > > The only other known device driver suffering for the issue is the > infiniband ipoib driver, I send a separate patch for it. > > I lack the broadcom h/w, but with infiniband the bug can be reproduced > with the following steps: > > - ensure ipv6 is enabled on the target device, and firewalld is running > (e.g. the module nf_conntrack_ipv6 is loaded) > - assign a static ip to the device > - shut down the firewall (e.g. try to remove the module nf_conntrack) > > For the brcmfmac driver most probably it is necessary being > disassociated from the AP before shutting down the firewall (but I > can't double check). This is probably why mac80211 does not suffer this > issue. > > The root cause for the issue could be actually a firmware issue, any > better clues are more than welcome! BTW, you should have added all this to the commit log. After reading the original description it left more questions open than answered them. -- Kalle Valo