[PATCH] Xentrace: Avoid Crash on Debug Build Xen

[Yosuke Iwamatsu <y-iwamatsu@ab.jp.nec.com>]

Mark Williamson wrote:
>          }
>          total_size += LOST_REC_SIZE;
>      }
> -
> -    ASSERT(bytes_to_wrap == calc_bytes_to_wrap(buf));
>  
>      if ( rec_size > bytes_to_wrap )
>      {
> @@ -484,8 +482,6 @@ void __trace_var(u32 event, int cycles, 
>          insert_lost_records(buf);
>      }
>  
> -    ASSERT(bytes_to_wrap == calc_bytes_to_wrap(buf));
> -
> 
>> Current xen-unstable (debug build) crashes when using xentrace command,
>> due to assertion failures. It seems assertion failures occur whenever
>> there exist lost records, and I don't see much reason to do this.
>> (Could anyone explain about these ASSERT lines ?)
> 
> These asserts appear to have originally been checking that bytes_to_wrap is 
> being calculated correctly...  It looks to me that the first assert 
> isoutdated though, because it clearly will fail if a record is lost.
> 
> Perhaps the second one ought to succed though, since the value of buf->prod 
> will have been appropriately updated by insert_lost_records()?

Indeed the second assert seems to always succeed.

> 
> Cheers,
> Mark
> 
>> The attached patch removes assertions to avoid system crashes,
>> and also fixes a mistake of an assignment statement.
>>
>> Regards,
>> -------------------
>> Yosuke Iwamatsu
>>         NEC Corporation
> 
> 
>