Re: XenVif div by zero on Tx path after resume.

["Durrant, Paul" <xadimgnik@xxxxxxxxx>]

On 28/04/2022 16:23, Martin Harvey wrote:
> -----Original Message-----
> From: Durrant, Paul <xadimgnik@xxxxxxxxx>
> Sent: 25 April 2022 10:15
> To: Martin Harvey <martin.harvey@xxxxxxxxxx>; paul@xxxxxxx; 
> win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: XenVif div by zero on Tx path after resume.
>
> > It then calls SyncRelease(). This runs the 'late' suspend callbacks and 
> > terminates the DPCs on other CPUs, thus allowing threads to be scheduled. It 
> > then lowers IRQL on the current CPU, which should mean a fall back to PASSIVE 
> > as SuspendTrigger() is only ever called from the dedicated thread (running 
> > FdoSuspend()).
> Nice try. The mutual exclusion for the late callbacks depends on the other 
> CPU's still spinning at dispatch - since plenty of other network processing 
> also happens at dispatch. You need to complete *all* the late callbacks before 
> releasing *any* of the CPU's from our DPC. One more step duly added in RFC 
> patch.
Ok, right... I broke it in:

-----
commit 9b7a47317031ddf5fab74311b24756c05bac72ae
Author: Paul Durrant <pdurrant@xxxxxxxxxx>
Date:   Mon Nov 30 13:52:09 2020 +0000

    Re-work the code in sync.c to provide per-CPU 'early' and 'late' 
callbacks...
    ... and then use these to drive the XENBUS_SUSPEND callbacks, 
rather than them
    being called directly from SuspendTrigger().

    Since the clients of the XENBUS_SUSPEND interface only expect one 
invocation
    of each callback, rather then one per-CPU, they are only invoked 
from the
    sync.c callback for CPU 0. A subsequent patch will introduce a 
function that
    must be called from the 'early' callback for each CPU.

    NOTE: The call to KeGetCurrentProcessorNumberEx() made in 
SyncRelease() is
          relocated to __SyncRelease(), as that is the place where the 
CPU index
          is actually used.

    Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
-----

I'll take a look at the RFC patch. Thanks for figuring this out.

  Paul

> MH.