On 8/19/21 11:29 AM, Jens Axboe wrote: > 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? > > 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. Pavel nudged me, and in the 5.15 branch we actually only do run rewait from the task itself. So this patch isn't needed, we can ignore it! Might just augment it with a comment, like it was done for submit. -- Jens Axboe
