From mboxrd@z Thu Jan 1 00:00:00 1970 From: Florian Fainelli Subject: Re: [PATCH net] net: systemport: Fix 64-bit stats deadlock Date: Tue, 12 Sep 2017 14:48:25 -0700 Message-ID: <23e3924f-7efc-efe5-4866-f552b1b0c97e@gmail.com> References: <1505247266-42195-1-git-send-email-f.fainelli@gmail.com> <1505252293.15310.151.camel@edumazet-glaptop3.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: netdev@vger.kernel.org, davem@davemloft.net, edumazet@google.com, jqiaoulk@gmail.com To: Eric Dumazet Return-path: Received: from mail-qk0-f196.google.com ([209.85.220.196]:36350 "EHLO mail-qk0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751477AbdILVsb (ORCPT ); Tue, 12 Sep 2017 17:48:31 -0400 Received: by mail-qk0-f196.google.com with SMTP id i14so7951641qke.3 for ; Tue, 12 Sep 2017 14:48:30 -0700 (PDT) In-Reply-To: <1505252293.15310.151.camel@edumazet-glaptop3.roam.corp.google.com> Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 09/12/2017 02:38 PM, Eric Dumazet wrote: > On Tue, 2017-09-12 at 13:14 -0700, Florian Fainelli wrote: >> We can enter a deadlock situation because there is no sufficient protection >> when ndo_get_stats64() runs in process context to guard against RX or TX NAPI >> contexts running in softirq, this can lead to the following lockdep splat and >> actual deadlock was experienced as well with an iperf session in the background >> and a while loop doing ifconfig + ethtool. > >> So just remove the u64_stats_update_begin()/end() pair in ndo_get_stats64() >> since it does not appear to be useful for anything. No inconsistency was >> observed with either ifconfig or ethtool, global TX counts equal the sum of >> per-queue TX counts on a 32-bit architecture. >> >> Fixes: 10377ba7673d ("net: systemport: Support 64bit statistics") >> Signed-off-by: Florian Fainelli >> --- >> drivers/net/ethernet/broadcom/bcmsysport.c | 3 --- >> 1 file changed, 3 deletions(-) >> >> diff --git a/drivers/net/ethernet/broadcom/bcmsysport.c b/drivers/net/ethernet/broadcom/bcmsysport.c >> index a6572b51435a..c3c53f6cd9e6 100644 >> --- a/drivers/net/ethernet/broadcom/bcmsysport.c >> +++ b/drivers/net/ethernet/broadcom/bcmsysport.c >> @@ -1735,11 +1735,8 @@ static void bcm_sysport_get_stats64(struct net_device *dev, >> stats->tx_packets += tx_packets; >> } >> >> - /* lockless update tx_bytes and tx_packets */ >> - u64_stats_update_begin(&priv->syncp); > > Yes, this u64_stats_update_begin()/u64_stats_update_end() is bogus > > But why do we even write on tx_bytes/tx_packets here ??? That's for the ethtool -S netdev stats copy (that's on me, I added that in the driver initial version), so yes, not very robust... > > Seems very wrong anyway. > > (ethtool -S does not call bcm_sysport_get_stats64() to refresh them ) Yes that might actually be the simplest way to get this fixed. > >> stats64->tx_bytes = stats->tx_bytes; >> stats64->tx_packets = stats->tx_packets; >> - u64_stats_update_end(&priv->syncp); >> >> do { >> start = u64_stats_fetch_begin_irq(&priv->syncp); > > -- Florian