Messages in this thread | | | From | Pavel Begunkov <> | Subject | Re: [RFC] exit: do exit_task_work() before shooting off mm | Date | Sun, 20 Dec 2020 14:42:10 +0000 |
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On 20/12/2020 13:58, Oleg Nesterov wrote: > On 12/20, Pavel Begunkov wrote: >> >> On 08/12/2020 01:37, Al Viro wrote: >>> On Thu, Dec 03, 2020 at 02:30:46AM +0000, Pavel Begunkov wrote: >>>> Handle task works and lock it earlier before it starts killing off >>>> task's resources like mm. io_uring makes use of it a lot and it'd >>>> nicer to have all added task_work finding tasks in a consistent state. > > I too do not understand this patch. task_work_add() will fail after > exit_task_work(). This means that, for example, exit_files() will use > schedule_delayed_work().
The first one? Between PF_EXITING and exit_task_work() do_exit() will kill mm/etc., I wanted to not see tasks half dismantled for task_works run in the exit_task_work(). Anyway, forget about it :)
>> One more moment, after we've set PF_EXITING any task_work_run() would be >> equivalent to exit_task_work() > > Yes, currently task_work_run() can not be called after exit_signals(). > And shouldn't be called imo ;) > >> io_uring >> may want (currently doesn't) to run works for cancellation purposes.t > > Please see https://lore.kernel.org/io-uring/20200407163816.GB9655@redhat.com/>> Shouldn't it be like below (not tested)? Also simplifies task_work_run(). > > I'd prefer the patch from the link above, but your version looks correct too.
I missed the thread, thanks! tbh, splitting into 2 functions looks better to me, but it's not like that matters
> However, I still think it would be better to not abuse task_work_run() too > much...
The problem is that io_uring cancels requests in exit_files() and some of them may be sitting in task_works, and we need to get them out of there to complete.
Also, I need to double check, but seems new requests may be added during and by cancellation because we did not yet set it to work_exited by the time (in exit_files()).
-- Pavel Begunkov
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