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.
Cheers
Trond
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