ATA/Cdrom(?) panic

[Alexander Motin]

On 11/16/11 16:14, Bjoern A. Zeeb wrote:
> On Wed, 16 Nov 2011, Alexander Motin wrote:
> 
>> Hi.
>>
>> On 11/16/11 08:43, Bjoern A. Zeeb wrote:
>>> we have seen this or a very similar panic for about 1 year now once in
>>> a while and I think I reported it before; this is FreeBSD as guest on
>>> vmware.   Seems it was a double panic this time.   Could someone please
>>> see what's going on there?    It was on 8.x-STABLE in the past and this
>>> is 8.2-RELEASE-p4.
>>
>> The part of code reporting "completing request directly" is IMHO broken
>> by design. It returns request completion before request will actually be
>> completed by lower levels without any knowledge of what's going on
>> there. There is kind of protection against double request completion,
>> but it looks like not always working. May be because that part of code
>> is not locked and nothing prevents that semaphore timeout and normal
>> request timeout/completion to happen simultaneously. It is surprising to
>> see even two traps same time, not sure what synchronized them so
>> precisely.
>>
>> Simple removing that semaphore timeout is not an option, because it will
>> cause deadlock when this wait happen within taskqueue thread that is
>> used to handle requests completion and abort that wait. Avoid waiting
>> inside taskqueue is also impossible without major rewrite. That's why
>> ATA_CAM drops that code completely.
> 
> So the bottom line of what you are saying is:
> 1) it's hard to fix right in 8
> 2) it's not an issue in 9 anymore at all?

Right.

-- 
Alexander Motin