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

[jianhai luan <jianhai.luan@xxxxxxxxxx>]

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

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