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
