Xen devel - Oct 2013 - 答复: Re: DomU's network interface will hung when Dom0 running 32bit

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.

Is it a timer to be set as less than ULONG_MAX/2 to avoid credit_timeout.expires
rolling over? But the problem is that we can not assure where jiffies start
from, and this probably results into current issue again.
I assume Jason''s patch fix this issue and this patch only uses
__mod_timer to add a timer with next_credit when the netback fails to send out
current available credits.

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

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