Re: [PATCH] IB/hfi1: Remove race conditions in user_sdma send path

[Sasha Levin <sashal@kernel.org>]

On Tue, Dec 18, 2018 at 04:00:22PM -0500, Michael J. Ruhl wrote:
>From: Michael J. Ruhl <michael.j.ruhl@intel.com>
>
>commit 28a9a9e83ceae2cee25b9af9ad20d53aaa9ab951 upstream
>
>Packet queue state is over used to determine SDMA descriptor
>availablitity and packet queue request state.
>
>cpu 0  ret = user_sdma_send_pkts(req, pcount);
>cpu 0  if (atomic_read(&pq->n_reqs))
>cpu 1  IRQ user_sdma_txreq_cb calls pq_update() (state to _INACTIVE)
>cpu 0        xchg(&pq->state, SDMA_PKT_Q_ACTIVE);
>
>At this point pq->n_reqs == 0 and pq->state is incorrectly
>SDMA_PKT_Q_ACTIVE.  The close path will hang waiting for the state
>to return to _INACTIVE.
>
>This can also change the state from _DEFERRED to _ACTIVE.  However,
>this is a mostly benign race.
>
>Remove the racy code path.
>
>Use n_reqs to determine if a packet queue is active or not.
>
>Cc: <stable@vger.kernel.org> # 4.19.x
>Reviewed-by: Mitko Haralanov <mitko.haralanov@intel.com>
>Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
>Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
>Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
>Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

I've queued all 3 to their respective trees, thank you.

--
Thanks,
Sasha