Re: [PATCH 7/9] io_uring: add per-task callback handler

[Jens Axboe <axboe@kernel.dk>]

On 2/23/20 7:58 AM, Jens Axboe wrote:
> On 2/23/20 7:49 AM, Jens Axboe wrote:
>>> Anyway, creds handling is too scattered across the code, and this do a
>>> lot of useless refcounting and bouncing. It's better to find it a
>>> better place in the near future.
>>
>> I think a good cleanup on top of this would be to move the personality
>> lookup to io_req_defer_prep(), and kill it from io_submit_sqe(). Now
>> __io_issue_sqe() does the right thing, and it'll just fall out nicely
>> with that as far as I can tell.
>>
>> Care to send a patch for that?
> 
> Since we also need it for non-deferral, how about just leaving the
> lookup in there and removing the assignment? That means we only do that
> juggling in one spot, which makes more sense. I think this should just
> be folded into the previous patch.

Tested, we need a ref grab on the creds when assigning since we're
dropped at the other end.


diff --git a/fs/io_uring.c b/fs/io_uring.c
index cead1a0602b4..d83f113f22fd 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4923,7 +4923,6 @@ static inline void io_queue_link_head(struct io_kiocb *req)
 static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 			  struct io_submit_state *state, struct io_kiocb **link)
 {
-	const struct cred *old_creds = NULL;
 	struct io_ring_ctx *ctx = req->ctx;
 	unsigned int sqe_flags;
 	int ret, id;
@@ -4938,14 +4937,12 @@ static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 
 	id = READ_ONCE(sqe->personality);
 	if (id) {
-		const struct cred *personality_creds;
-
-		personality_creds = idr_find(&ctx->personality_idr, id);
-		if (unlikely(!personality_creds)) {
+		req->work.creds = idr_find(&ctx->personality_idr, id);
+		if (unlikely(!req->work.creds)) {
 			ret = -EINVAL;
 			goto err_req;
 		}
-		old_creds = override_creds(personality_creds);
+		get_cred(req->work.creds);
 	}
 
 	/* same numerical values with corresponding REQ_F_*, safe to copy */
@@ -4957,8 +4954,6 @@ static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 err_req:
 		io_cqring_add_event(req, ret);
 		io_double_put_req(req);
-		if (old_creds)
-			revert_creds(old_creds);
 		return false;
 	}
 
@@ -5019,8 +5014,6 @@ static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		}
 	}
 
-	if (old_creds)
-		revert_creds(old_creds);
 	return true;
 }
 

-- 
Jens Axboe