On 24/07/2020 15:46, Pavel Begunkov wrote: > On 24/07/2020 01:24, Jens Axboe wrote: >> On 7/23/20 4:16 PM, Jens Axboe wrote: >>> On 7/23/20 12:12 PM, Pavel Begunkov wrote: >>>> poll_add can have req->work initialised, which will be overwritten in >>>> __io_arm_poll_handler() because of the union. Luckily, hash_node is >>>> zeroed in the end, so the damage is limited to lost put for work.creds, >>>> and probably corrupted work.list. >>>> >>>> That's the easiest and really dirty fix, which rearranges members in the >>>> union, arm_poll*() modifies and zeroes only work.files and work.mm, >>>> which are never taken for poll add. >>>> note: io_kiocb is exactly 4 cachelines now. >>> >>> I don't think there's a way around moving task_work out, just like it > > +hash_node. I was thinking to do apoll alloc+memcpy as for rw, but this > one is ugly. > >>> was done on 5.9. The problem is that we could put the environment bits >>> before doing task_work_add(), but we might need them if the subsequent >>> queue ends up having to go async. So there's really no know when we can >>> put them, outside of when the request finishes. Hence, we are kind of >>> SOL here. >> >> Actually, if we do go async, then we can just grab the environment >> again. We're in the same task at that point. So maybe it'd be better to >> work on ensuring that the request is either in the valid work state, or >> empty work if using task_work. >> >> Only potential complication with that is doing io_req_work_drop_env() >> from the waitqueue handler, at least the ->needs_fs part won't like that >> too much. > > Considering that work->list is removed before executing io_wq_work, it > should work. And if done only for poll_add, which needs nothing and ends up > with creds, there shouldn't be any problems. I'll try this out Except for custom ->creds assigned at the beginning with the personality feature. Does poll ever use it? -- Pavel Begunkov
