From mboxrd@z Thu Jan 1 00:00:00 1970 From: jianhai luan Subject: Re: DomU's network interface will hung when Dom0 running 32bit Date: Tue, 15 Oct 2013 10:44:49 +0800 Message-ID: <525CAC21.5040202@oracle.com> References: <52590DFE.6080203@oracle.com> <20131014111958.GE11739@zion.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Ian Campbell , xen-devel@lists.xenproject.org, netdev@vger.kernel.org To: Wei Liu Return-path: Received: from aserp1040.oracle.com ([141.146.126.69]:46260 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755122Ab3JOCpB (ORCPT ); Mon, 14 Oct 2013 22:45:01 -0400 In-Reply-To: <20131014111958.GE11739@zion.uk.xensource.com> Sender: netdev-owner@vger.kernel.org List-ID: On 2013-10-14 19:19, Wei Liu wrote: > On Sat, Oct 12, 2013 at 04:53:18PM +0800, jianhai luan wrote: >> Hi Ian, >> I meet the DomU's network interface hung issue recently, and have >> been working on the issue from that time. I find that DomU's network >> interface, which send lesser package, will hung if Dom0 running >> 32bit and DomU's up-time is very long. I think that one jiffies >> overflow bug exist in the function tx_credit_exceeded(). >> I know the inline function time_after_eq(a,b) will process jiffies >> overflow, but the function have one limit a should little that (b + >> MAX_SIGNAL_LONG). If a large than the value, time_after_eq will >> return false. The MAX_SINGNAL_LONG should be 0x7fffffff at 32-bit >> machine. >> If DomU's network interface send lesser package (<0.5k/s if >> jiffies=250 and credit_bytes=ULONG_MAX), jiffies will beyond out >> (credit_timeout.expires + MAX_SIGNAL_LONG) and time_after_eq(now, >> next_credit) will failure (should be true). So one timer which will >> not be trigger in short time, and later process will be aborted when >> timer_pending(&vif->credit_timeout) is true. The result will be >> DomU's network interface will be hung in long time (> 40days). >> Please think about the below scenario: >> Condition: >> Dom0 running 32-bit and HZ = 1000 >> vif->credit_timeout->expire = 0xffffffff, vif->remaining_credit >> = 0xffffffff, vif->credit_usec=0 jiffies=0 >> vif receive lesser package (DomU send lesser package). If the >> value is litter than 2K/s, consume 4G(0xffffffff) will need 582.55 >> hours. jiffies will large than 0x7ffffff. we guess jiffies = >> 0x800000ff, time_after_eq(0x800000ff, 0xffffffff) will failure, and >> one time which expire is 0xfffffff will be pended into system. So >> the interface will hung until jiffies recount 0xffffffff (that will >> need very long time). > If I'm not mistaken you meant time_after_eq(now, next_credit) in > netback. How does next_credit become 0xffffffff? I only assume the value is 0xfffffff, and the value of next_credit isn't point. If the delta between now and next_credit larger than ULONG_MAX, time_after_eq will do wrong judge. > > Wei. > >> If some error exist in above explain, please help me point it out. >> >> Thanks, >> Jason