Gilles Chanteperdrix wrote:
> Jan Kiszka wrote:
>> Gilles Chanteperdrix wrote:
>>> Jan Kiszka wrote:
>>>> Gilles Chanteperdrix wrote:
>>>>> Jan Kiszka wrote:
>>>>>> Gilles Chanteperdrix wrote:
>>>>>>> Ok for returning -EINTR, it is documented. Kernel-space is not so
>>>>>>> different from user-space, rt_task_unblock could wake-up a kernel-space
>>>>>>> task blocked in a call to rt_cond_wait.
>>>>>>>
>>>>>>> However, if the epilogue returns an error, we must return it.
>>>>>>>
>>>>>> OK for this. Pushed an update, but I also modified it further to avoid
>>>>>> returning without the mutex lock unless that one is also failing. Maybe
>>>>>> in-kernel POSIX requires the same fix, will check.
>>>>> Still not OK. You should reacquire the mutex only if the error is 0,
>>>>> -ETIMEDOUT or -EINTR. With any other error, we do not know if we can
>>>>> call the epilogue safely.
>>>> We _must_ reacquire the mutex - but, granted, we actually have to take
>>>> care of invalid cond objects. Lot's of bugs...
>>> No. If the error is another error than 0, -ETIMEDOUT, or -EINTR, it
>>> means that the error was detected prior to freeing the mutex. So, we do
>>> not have to re-acquire the mutex. Quoting POSIX:
>>>
>>> "Except in the case of [ETIMEDOUT], all these error checks shall act as
>>> if they were performed immediately at the beginning of processing for
>>> the function and shall cause an error return, in effect, prior to
>>> modifying the state of the mutex specified by mutex or the condition
>>> variable specified by cond."
>>>
>>> POSIX does not talk about -EINTR, because it states that in this case,
>>> we should return 0 to the application.
>> OK, but EIDRM was missing in your list. Will adjust both patches.
> 
> No, EIDRM is part of the "other errors than ETIMEDOUT and 0"
> 

I interpret the spec fairly differently here: It states that we have to
leave the mutex state behind *as if* the error was already detected on
entry - thus we are expected to restore its state.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

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