net/mlx5: Support throttled commands from async API

Currently, commands that qualify as throttled can't be used via the
async API. That's due to the fact that the throttle semaphore can sleep
but the async API can't.

This patch allows throttling in the async API by using the tentative
variant of the semaphore and upon failure (semaphore at 0) returns EBUSY
to signal to the caller that they need to wait for the completion of
previously issued commands.

Furthermore, make sure that the semaphore is released in the callback.
Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Cc: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Message-Id: <20240816090159.1967650-2-dtatulea@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>

drivers/net/ethernet/mellanox/mlx5/core/cmd.c

@@ -1882,11 +1882,13 @@ static int cmd_exec(struct mlx5_core_dev *dev, void *in, int in_size, void *out,
 
 	throttle_op = mlx5_cmd_is_throttle_opcode(opcode);
 	if (throttle_op) {
-		/* atomic context may not sleep */
-		if (callback)
-			return -EINVAL;
+		if (callback) {
+			if (down_trylock(&dev->cmd.vars.throttle_sem))
+				return -EBUSY;
+		} else {
 			down(&dev->cmd.vars.throttle_sem);
 		}
+	}
 
 	pages_queue = is_manage_pages(in);
 	gfp = callback ? GFP_ATOMIC : GFP_KERNEL;
@@ -2091,10 +2093,19 @@ static void mlx5_cmd_exec_cb_handler(int status, void *_work)
 {
 	struct mlx5_async_work *work = _work;
 	struct mlx5_async_ctx *ctx;
+	struct mlx5_core_dev *dev;
+	u16 opcode;
 
 	ctx = work->ctx;
-	status = cmd_status_err(ctx->dev, status, work->opcode, work->op_mod, work->out);
+	dev = ctx->dev;
+	opcode = work->opcode;
+	status = cmd_status_err(dev, status, work->opcode, work->op_mod, work->out);
 	work->user_callback(status, work);
+	/* Can't access "work" from this point on. It could have been freed in
+	 * the callback.
+	 */
+	if (mlx5_cmd_is_throttle_opcode(opcode))
+		up(&dev->cmd.vars.throttle_sem);
 	if (atomic_dec_and_test(&ctx->num_inflight))
 		complete(&ctx->inflight_done);
 }