On 1/29/2020 8:34 PM, Jens Axboe wrote: > On 1/29/20 7:23 AM, Pavel Begunkov wrote: >>>>> The override_creds(personality_creds) has changed current->cred >>>>> and get_current_cred() will just pick it up as in the default case. >>>>> >>>>> This would make the patch much simpler and allows put_cred() to be >>>>> in io_put_work() instead of __io_req_aux_free() as explained above. >>>>> >>>> >>>> It's one extra get_current_cred(). I'd prefer to find another way to >>>> clean this up. >>> >>> As far as I can see it avoids a get_cred() in the IOSQE_PERSONALITY case >>> and the if (!req->work.creds) for both cases. >> >> Great, that you turned attention to that! override_creds() is already >> grabbing a ref, so it shouldn't call get_cred() there. >> So, that's a bug. > > It's not though - one is dropped in that function, the other when the > request is freed. So we do need two references to it. With the proposed > change to keep the override_creds() variable local for that spot we > don't, and the get_cred() can then go. You're right here. It seems, it was too much looking at the same code :) > >> It could be I'm wrong with the statement above, need to recheck all this >> code to be sure. > > I think you are :-) Considering above, there shouldn't be much difference indeed. One extra rcu_dereference() in get_current_creds() instead of get_cred(), but that's nothing. Later we can hide one get by using submission state from the long patchset, I sent a while ago. > >> BTW, io_req_defer_prep() may be called twice for a req, so you will >> reassign it without putting a ref. It's safer to leave NULL checks. At >> least, until I've done reworking and fixing preparation paths. > > Agree, the NULL checks are safer and we should keep them. > > Going through the rest of this thread, I'm making the following changes: > > - ID must be > 0. I like that change, as we don't need an sqe flag to > select personality then, and it also makes it obvious that id == 0 is > just using current creds. > > - Fixed the missing put_cred() in the teardown > > - Use a local variable in io_submit_sqe() instead of assigning the > creds to req->work.creds there > > - Use cyclic idr allocation > > I'm going to fold in as appropriate. If there are fixes needed on top of > that, let's do them separately. > -- Pavel Begunkov
