• Dries Kimpe's avatar
    Fix BMI memcache issues · 6d96c9ba
    Dries Kimpe authored
    Patch from Jingwang Zhang.
    
    Here is our use case, and we are using the BMI code in OrangeFS 2.8.6:
    
    1.       Malloc a buffer and write something to it.
    
    2.       Send the buffer using BMI routines.
    
    3.       Free the buffer and goto step 1
    
    And here we found the following problem: We found that the messages
    captured using ibdump is corrupt in iteration 2. It became a mixture of
    data from iteration 1 and iteration 2.
    
    Here is some analysis we did: We noticed that when the data corruption
    occurs, the buffer always point to the same virtual address. And after
    checking with the BMI code, we found that the memcache code will keep
    the buffer registered(to ibverbs) and use virtual address to determine
    whether a registered buffer could be reused or not later.
    
    However I think the memcache shouldn't keep the buffer registered,
    because that the user might free this buffer, and when the user did free
    and re-allocate the buffer, there might be a false match which might
    lead to data corruption.
    
    So at first, we tested the code with "define ENABLE_MEMCACHE 0" to
    disable the memcache. And then the test passed, so it is proven that the
    data corruption is caused by memcache. However, performance will be
    affected if the memcache is disabled completely.
    
    Finally we formatted the attached patch to solve the problem. It fixes
    the broken code in the clauses when memcache is disabled. And it
    deregister the buffer whenever its use-count drops to 0 and register it
    when it is used again.
    6d96c9ba
mem.c 11.4 KB