On 8/19/21 11:36 AM, Hao Xu wrote: > 在 2021/8/20 上午1:29, Jens Axboe 写道: >> On 8/19/21 11:26 AM, Hao Xu wrote: >>> 在 2021/8/19 下午11:48, Jens Axboe 写道: >>>> We have two checks of task->flags & PF_EXITING left: >>>> >>>> 1) In io_req_task_submit(), which is called in task_work and hence always >>>> in the context of the original task. That means that >>>> req->task == current, and hence checking ->flags is totally fine. >>>> >>>> 2) In io_poll_rewait(), where we need to stop re-arming poll to prevent >>>> it interfering with cancelation. Here, req->task is not necessarily >>>> current, and hence the check is racy. Use the ctx refs state instead >>>> to check if we need to cancel this request or not. >>> Hi Jens, >>> I saw cases that io_req_task_submit() and io_poll_rewait() in one >>> function, why one is safe and the other one not? btw, it seems both two >>> executes in task_work context..and task_work_add() may fail and then >>> work goes to system_wq, is that case safe? > I've got answer for the second question.. >> >> io_req_task_submit() is guaranteed to be run in the task that is req->task, >> io_poll_rewait() is not. The latter can get called from eg the poll >> waitqueue handling, which is not run from the task in question. > I only found io_poll_rewait() call in io_async_task_func() and > io_poll_task_func(), both are in task_work Yeah see followup, my information was outdated, we only do rewait from the right context at this point. Hence the PF_EXITING check is actually fine. -- Jens Axboe
