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Re: [Xen-devel] [PATCH 1/1] xen/gnttab: print log at level XENLOG_ERR before panic


  • To: <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Thu, 25 Apr 2019 14:17:52 +0100
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  • Delivery-date: Thu, 25 Apr 2019 13:20:24 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 25/04/2019 14:10, Jan Beulich wrote:
>>>> On 23.04.19 at 18:00, <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 23/04/2019 12:47, George Dunlap wrote:
>>> On 4/23/19 11:37 AM, Andrew Cooper wrote:
>>>> On 22/04/2019 13:39, Dongli Zhang wrote:
>>>>> Print log at level XENLOG_ERR (instead XENLOG_INFO) as domain_crash()
>>>>> indicates there is fatal error.
>>>>>
>>>>> Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
>>>>> ---
>>>>>  xen/common/grant_table.c | 2 +-
>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
>>>>> index 80728ea..725c618 100644
>>>>> --- a/xen/common/grant_table.c
>>>>> +++ b/xen/common/grant_table.c
>>>>> @@ -1282,7 +1282,7 @@ unmap_common(
>>>>>      if ( unlikely((rd = rcu_lock_domain_by_id(dom)) == NULL) )
>>>>>      {
>>>>>          /* This can happen when a grant is implicitly unmapped. */
>>>>> -        gdprintk(XENLOG_INFO, "Could not find domain %d\n", dom);
>>>>> +        gdprintk(XENLOG_ERR, "Could not find domain %d\n", dom);
>>>> While I agree with the change in principle, what does this actually do? 
>>>> The entire printk() is compiled out in release builds, and debug builds
>>>> log all messages.
>>> ...by default; but presumably you can turn that down, right?
>> Yes you can, but a) noone does, because these are debug builds and b)
>> that isn't the point.  If we care about this message being printed, it
>> mustn’t be a gdprintk().
>>
>> It either wants to turn into a gprintk() at XENLOG_INFO, or wants
>> deleting entirely, but simply shuffling the exact level for a gdprintk()
>> is tantamount to useless.
> FWIW I agree, and I think there are quite a few more candidates of
> debug messages that would better go away, and should probably
> have been stripped off before the original commit introducing them.
>
> The one reason not to drop the message here, but to switch to
> gprintk(), is the adjacent domain_crash(). This, however, then is
> a reason to give it a log level above INFO.

I still have a series I need to refresh and repost which causes
domain_crash() to take a XENLOG_G_ERR print message, specifically so it
is not possible to ever get a domain_crash() without at least a hint of
what went wrong.

~Andrew

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