Hi
I was evaluating whether it is feasible to use QAT with dm-crypt (the
answer is that it is not - QAT is slower than AES-NI for this type of
workload; QAT starts to be benefical for encryption requests longer than
64k). And I got some deadlocks.
The reason for the deadlocks is this: suppose that one of the "if"
conditions in "qat_alg_send_message_maybacklog" is true and we jump to the
"enqueue" label. At this point, an interrupt comes in and clears all
pending messages. Now, the interrupt returns, we grab backlog->lock, add
the message to the backlog, drop backlog->lock - and there is no one to
remove the backlogged message out of the list and submit it.
I fixed it with this patch - with this patch, the test passes and there
are no longer any deadlocks. I didn't want to add a spinlock to the hot
path, so I take it only if some of the condition suggests that queuing may
be required.
Signed-off-by: Mikulas Patocka <mpato...@redhat.com>
Cc: sta...@vger.kernel.org
---
drivers/crypto/intel/qat/qat_common/qat_algs_send.c | 31 ++++++++++++--------
1 file changed, 20 insertions(+), 11 deletions(-)
Index: linux-2.6/drivers/crypto/intel/qat/qat_common/qat_algs_send.c
===================================================================
--- linux-2.6.orig/drivers/crypto/intel/qat/qat_common/qat_algs_send.c
+++ linux-2.6/drivers/crypto/intel/qat/qat_common/qat_algs_send.c
@@ -40,16 +40,6 @@ void qat_alg_send_backlog(struct qat_ins
spin_unlock_bh(&backlog->lock);
}
-static void qat_alg_backlog_req(struct qat_alg_req *req,
- struct qat_instance_backlog *backlog)
-{
- INIT_LIST_HEAD(&req->list);
-
- spin_lock_bh(&backlog->lock);
- list_add_tail(&req->list, &backlog->list);
- spin_unlock_bh(&backlog->lock);
-}
-
static int qat_alg_send_message_maybacklog(struct qat_alg_req *req)
{
struct qat_instance_backlog *backlog = req->backlog;
@@ -71,8 +61,27 @@ static int qat_alg_send_message_maybackl
return -EINPROGRESS;
enqueue:
- qat_alg_backlog_req(req, backlog);
+ spin_lock_bh(&backlog->lock);
+
+ /* If any request is already backlogged, then add to backlog list */
+ if (!list_empty(&backlog->list))
+ goto enqueue2;
+ /* If ring is nearly full, then add to backlog list */
+ if (adf_ring_nearly_full(tx_ring))
+ goto enqueue2;
+
+ /* If adding request to HW ring fails, then add to backlog list */
+ if (adf_send_message(tx_ring, fw_req))
+ goto enqueue2;
+
+ spin_unlock_bh(&backlog->lock);
+ return -EINPROGRESS;
+
+enqueue2:
+ list_add_tail(&req->list, &backlog->list);
+
+ spin_unlock_bh(&backlog->lock);
return -EBUSY;
}
--
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