On Jul 22, 2015, at 5:15 PM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>
> On Jul 22, 2015, at 5:14 PM, Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> wrote:
>
>> On Wed, Jul 22, 2015 at 4:40 PM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>>> Hi Trond-
>>>
>>>
>>> On Jul 22, 2015, at 4:36 PM, Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> wrote:
>>>
>>>> xprt_alloc_bc_request() cannot call xprt_free_bc_request() without
>>>> deadlocking, since it already holds the xprt->bc_pa_lock.
>>>>
>>>> Reported-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>>>> Fixes: 0d2a970d0ae55 ("SUNRPC: Fix a backchannel race")
>>>> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
>>>
>>> That’s exactly what I did as a basic fix, and I can report that
>>> it successfully avoids the deadlock.
>>>
>>> If xprt_alloc_bc_request() no longer calls xprt_free_bc_request(),
>>> are the accounting changes introduced by 0d2a970d0ae55 still
>>> necessary?
>>
>> The accounting changes are there to fix the race that Christoph
>> reported in which a valid backchannel request can be rejected by the
>> RPC layer if it happens to come in after the reply to the previous
>> request was sent, but before xprt_free_bc_request has completed. I
>> would therefore expect them still to be needed.
>>
>> That said, I just noticed that the bc_free_count was being incorrectly
>> maintained. Should be fixed with v2 of the patch series.
>
> I will get v2 in front of the tester who found this issue.
The v2 fix appears solid. Thanks!
--
Chuck Lever
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