Re: [Xen-devel] [PATCH] xen/x86: add diagnostic printout to xen_mc_flush() in case of error

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 11/27/18 2:46 AM, Juergen Gross wrote:
> On 26/11/2018 21:11, Boris Ostrovsky wrote:
>> On 11/23/18 11:24 AM, Juergen Gross wrote:
>>> Failure of an element of a Xen multicall is signalled via a WARN()
>>> only unless the kernel is compiled with MC_DEBUG. It is impossible to
>> s/unless/if
>>
>>
>>> know which element failed and why it did so.
>>>
>>> Change that by printing the related information even without MC_DEBUG,
>>> even if maybe in some limited form (e.g. without information which
>>> caller produced the failing element).
>>>
>>> Move the printing out of the switch statement in order to have the
>>> same information for a single call.
>>>
>>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>>> ---
>>>  arch/x86/xen/multicalls.c | 35 ++++++++++++++++++++---------------
>>>  1 file changed, 20 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/arch/x86/xen/multicalls.c b/arch/x86/xen/multicalls.c
>>> index 2bce7958ce8b..0766a08bdf45 100644
>>> --- a/arch/x86/xen/multicalls.c
>>> +++ b/arch/x86/xen/multicalls.c
>>> @@ -69,6 +69,11 @@ void xen_mc_flush(void)
>>>  
>>>     trace_xen_mc_flush(b->mcidx, b->argidx, b->cbidx);
>>>  
>>> +#if MC_DEBUG
>>> +   memcpy(b->debug, b->entries,
>>> +          b->mcidx * sizeof(struct multicall_entry));
>>> +#endif
>>> +
>>>     switch (b->mcidx) {
>>>     case 0:
>>>             /* no-op */
>>> @@ -87,32 +92,34 @@ void xen_mc_flush(void)
>>>             break;
>>>  
>>>     default:
>>> -#if MC_DEBUG
>>> -           memcpy(b->debug, b->entries,
>>> -                  b->mcidx * sizeof(struct multicall_entry));
>>> -#endif
>>> -
>>>             if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
>>>                     BUG();
>>>             for (i = 0; i < b->mcidx; i++)
>>>                     if (b->entries[i].result < 0)
>>>                             ret++;
>>> +   }
>>>  
>>> +   if (WARN_ON(ret)) {
>>> +           pr_err("%d of %d multicall(s) failed: cpu %d\n",
>>> +                  ret, b->mcidx, smp_processor_id());
>>> +           for (i = 0; i < b->mcidx; i++) {
>>> +                   if (b->entries[i].result < 0) {
>>>  #if MC_DEBUG
>>> -           if (ret) {
>>> -                   printk(KERN_ERR "%d multicall(s) failed: cpu %d\n",
>>> -                          ret, smp_processor_id());
>>> -                   dump_stack();
>>> -                   for (i = 0; i < b->mcidx; i++) {
>>> -                           printk(KERN_DEBUG "  call %2d/%d: op=%lu 
>>> arg=[%lx] result=%ld\t%pF\n",
>>> -                                  i+1, b->mcidx,
>>> +                           pr_err("  call %2d: op=%lu arg=[%lx] 
>>> result=%ld\t%pF\n",
>>> +                                  i + 1,
>>>                                    b->debug[i].op,
>>>                                    b->debug[i].args[0],
>>>                                    b->entries[i].result,
>>>                                    b->caller[i]);
>>> +#else
>>> +                           pr_err("  call %2d: op=%lu arg=[%lx] 
>>> result=%ld\n",
>>> +                                  i + 1,
>>> +                                  b->entries[i].op,
>>> +                                  b->entries[i].args[0],
>>> +                                  b->entries[i].result);
>>> +#endif
>> Doesn't (non-debug) hypervisor corrupt op and args?
> No. Only debug hypervisor does so.
>
> See my patch (and rather lengthy discussion) on xen-devel:
>
> https://lists.xen.org/archives/html/xen-devel/2018-11/msg02714.html

Yes, I saw that later, after I responded to the patch.


>
>> (Also, we don't really need to print anything when b->entries[i].result
>> == 0)
> Right. Did you miss the:

I did.

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

(with commit message fixed)



>
> +                     if (b->entries[i].result < 0) {
>
> above?
>
>
> Juergen


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel