On 25 October 2016 at 17:58, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Tuesday, October 25, 2016 5:31:57 PM CEST Binoy Jayan wrote: >> static int __hns_roce_cmd_mbox_wait(struct hns_roce_dev *hr_dev, u64 in_param, >> u64 out_param, unsigned long in_modifier, >> @@ -198,11 +218,12 @@ static int __hns_roce_cmd_mbox_wait(struct hns_roce_dev *hr_dev, u64 in_param, >> struct hns_roce_cmdq *cmd = &hr_dev->cmd; >> struct device *dev = &hr_dev->pdev->dev; >> struct hns_roce_cmd_context *context; >> - int ret = 0; >> + int orig_free_head, ret = 0; >> + >> + wait_event(cmd->wq, (orig_free_head = atomic_free_node(cmd, -1)) != -1); >> >> spin_lock(&cmd->context_lock); >> - WARN_ON(cmd->free_head < 0); >> - context = &cmd->context[cmd->free_head]; >> + context = &cmd->context[orig_free_head]; >> context->token += cmd->token_mask + 1; >> cmd->free_head = context->next; >> spin_unlock(&cmd->context_lock); >> > > You get the lock in atomic_free_node() and then again right after that. > Why not combine the two and only take the lock inside of that > function that returns a context? Hi Arnd, I couldn't figure out a way to wait for a node to be free followed by acquiring a lock in an atomic fashion. If the lock is acquired after the wait_event, there could be race between the wait_event and acquiring the lock. If the lock is acquired before the wait_event, the process may goto sleep with the lock held which is not desired. Could you suggest me of some way to circumvent this? -Binoy -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
