Message-ID: <20131015100624.GB29436@zion.uk.xensource.com>
Date:	Tue, 15 Oct 2013 11:06:24 +0100
From:	Wei Liu <wei.liu2@...rix.com>
To:	jianhai luan <jianhai.luan@...cle.com>
CC:	Ian Campbell <Ian.Campbell@...rix.com>,
	Wei Liu <wei.liu2@...rix.com>,
	<xen-devel@...ts.xenproject.org>, <netdev@...r.kernel.org>,
	ANNIE LI <annie.li@...cle.com>
Subject: Re: DomU's network interface will hung when Dom0 running 32bit

On Tue, Oct 15, 2013 at 05:34:57PM +0800, jianhai luan wrote:
> 
> On 2013-10-15 16:43, Ian Campbell wrote:
> >On Tue, 2013-10-15 at 10:44 +0800, jianhai luan wrote:
> >>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.
> >So it sounds like we need a timer which is independent of the traffic
> >being sent to keep credit_timeout.expires rolling over.
> >
> >Can you propose a patch?
> 
> Because credit_timeout.expire always after jiffies, i judge the
> value over the range of time_after_eq() by time_before(now,
> vif->credit_timeout.expires). please check the patch.

I don't think this really fix the issue for you. You still have chance
that now wraps around and falls between expires and next_credit. In that
case it's stalled again.

Wei.
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