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 <jgr...@suse.com>
>> ---
>> 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
>
> (Also, we don't really need to print anything when b->entries[i].result
> == 0)
Right. Did you miss the:
+ if (b->entries[i].result < 0) {
above?
Juergen
