Re: [Xen-devel] DomU's network interface will hung when Dom0 running 32bit

[jianhai luan <jianhai.luan@xxxxxxxxxx>]

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.
> Ian.
>
> > > Wei.
> > >
> > > >     If some error exist in above explain, please help me point it out.
> > > >
> > > > Thanks,
> > > > Jason

Attachment: 0001-Process-the-wrong-judge-of-time_after_eq.patch
Description: Text document

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