From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Begunkov Subject: Re: IORING_REGISTER_CREDS[_UPDATE]() and credfd_create()? Date: Wed, 29 Jan 2020 20:46:16 +0300 Message-ID: References: <688e187a-75dd-89d9-921c-67de228605ce@samba.org> <1ac31828-e915-6180-cdb4-36685442ea75@kernel.dk> <0d4f43d8-a0c4-920b-5b8f-127c1c5a3fad@kernel.dk> <2d7e7fa2-e725-8beb-90b9-6476d48bdb33@gmail.com> <6c401e23-de7c-1fc1-4122-33d53fcf9700@kernel.dk> <35eebae7-76dd-52ee-58b2-4f9e85caee40@kernel.dk> <6e5ab6bf-6ff1-14df-1988-a80a7c6c9294@gmail.com> <2019e952-df2a-6b57-3571-73c525c5ba1a@kernel.dk> <0df4904f-780b-5d5f-8700-41df47a1b470@kernel.dk> <5406612e-299d-9d6e-96fc-c962eb93887f@gmail.com> <821243e7-b470-ad7a-c1a5-535bee58e76d@samba.org> <9a419bc5-4445-318d-87aa-1474b49266dd@gmail.com> <40d52623-5f9c-d804-cdeb-b7da6b13cb4f@samba.org> <3e1289de-8d8e-49cf-cc9f-fb7bc67f35d5@gmail.com> <9aef3b3b-7e71-f7f1-b366-2517b4d52719@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <9aef3b3b-7e71-f7f1-b366-2517b4d52719-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> Content-Language: en-US Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Jens Axboe , Stefan Metzmacher Cc: io-uring , Linux API Mailing List List-Id: linux-api@vger.kernel.org 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