On 7/24/20 6:52 AM, Pavel Begunkov wrote: > 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? It's kind of annoying how we don't have a def->needs_creds, because lots of things would never use it. For poll, it wouldn't be used at all, which makes this issue doubly annoying. -- Jens Axboe
