Re: [dm-devel] [PATCH] 2.6.12-rc6: fix rh_dec()/rh_inc() race in dm-raid1.c

["Jun'ichi Nomura" <j-nomura ce jp nec com>]

Hi Jon,

Jonathan E Brassow wrote:
> could this be solved by doing your patch in rh_dec and just moving the
> atomic_inc in rh_inc?  The reason I ask is that the mark_region log
> call can block.

No.
Unless they are serialized, it's possible that rh_inc() will see the
state RH_DIRTY, while rh_dec change it to RH_CLEAN.
As a result, the region which has I/O in-flight may be freed.

Is it reasonable to call mark_region() unconditionally?
Then we can call it outside of the lock.

>>    CPU0                                   CPU1
>>
>> -----------------------------------------------------------------------
>> -------
>>    rh_dec()
>>      if (atomic_dec_and_test(pending))
>>         <the region is still marked dirty>
           if (atomic_read(pending)==0)
>>                                           rh_inc()
>>                                             atomic_inc(pending)
>>                                             if the region is clean
>>                                                mark the region dirty
>>                                                and remove from clean list
                                               else do nothing
>>         mark the region clean
>>         and move to clean list