io_uring: refactor poll arm error handling

__io_arm_poll_handler() errors parsing is a horror, in case it failed it
returns 0 and the caller is expected to look at ipt.error, which already
led us to a number of problems before.

When it returns a valid mask, leave it as it's not, i.e. return 1 and
store the mask in ipt.result_mask. In case of a failure that can be
handled inline return an error code (negative value), and return 0 if
__io_arm_poll_handler() took ownership of the request and will complete
it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/018cacdaef5fe95d7dc56b32e85d752cab7607f6.1655990418.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/poll.c b/io_uring/poll.c
index 80113b0..3f3ae3b 100644 (file)
--- a/io_uring/poll.c
+++ b/io_uring/poll.c
@@ -435,6 +435,12 @@ static void io_poll_queue_proc(struct file *file, struct wait_queue_head *head,
                        (struct io_poll **) &pt->req->async_data);
 }
 
+/*
+ * Returns 0 when it's handed over for polling. The caller owns the requests if
+ * it returns non-zero, but otherwise should not touch it. Negative values
+ * contain an error code. When the result is >0, the polling has completed
+ * inline and ipt.result_mask is set to the mask.
+ */
 static int __io_arm_poll_handler(struct io_kiocb *req,
                                 struct io_poll *poll,
                                 struct io_poll_table *ipt, __poll_t mask)
@@ -461,6 +467,17 @@ static int __io_arm_poll_handler(struct io_kiocb *req,
        atomic_set(&req->poll_refs, 1);
        mask = vfs_poll(req->file, &ipt->pt) & poll->events;
 
+       if (unlikely(ipt->error || !ipt->nr_entries)) {
+               io_poll_remove_entries(req);
+
+               if (mask && (poll->events & EPOLLET)) {
+                       ipt->result_mask = mask;
+                       return 1;
+               } else {
+                       return ipt->error ?: -EINVAL;
+               }
+       }
+
        if (mask &&
           ((poll->events & (EPOLLET|EPOLLONESHOT)) == (EPOLLET|EPOLLONESHOT))) {
                io_poll_remove_entries(req);
@@ -469,25 +486,12 @@ static int __io_arm_poll_handler(struct io_kiocb *req,
                return 1;
        }
 
-       if (!mask && unlikely(ipt->error || !ipt->nr_entries)) {
-               io_poll_remove_entries(req);
-               if (!ipt->error)
-                       ipt->error = -EINVAL;
-               return 0;
-       }
-
        if (req->flags & REQ_F_HASH_LOCKED)
                io_poll_req_insert_locked(req);
        else
                io_poll_req_insert(req);
 
        if (mask && (poll->events & EPOLLET)) {
-               /* can't multishot if failed, just queue the event we've got */
-               if (unlikely(ipt->error || !ipt->nr_entries)) {
-                       poll->events |= EPOLLONESHOT;
-                       req->apoll_events |= EPOLLONESHOT;
-                       ipt->error = 0;
-               }
                __io_poll_execute(req, mask);
                return 0;
        }
@@ -582,9 +586,8 @@ int io_arm_poll_handler(struct io_kiocb *req, unsigned issue_flags)
        io_kbuf_recycle(req, issue_flags);
 
        ret = __io_arm_poll_handler(req, &apoll->poll, &ipt, mask);
-       if (ret || ipt.error)
-               return ret ? IO_APOLL_READY : IO_APOLL_ABORTED;
-
+       if (ret)
+               return ret > 0 ? IO_APOLL_READY : IO_APOLL_ABORTED;
        trace_io_uring_poll_arm(req, mask, apoll->poll.events);
        return IO_APOLL_OK;
 }
@@ -815,16 +818,11 @@ int io_poll_add(struct io_kiocb *req, unsigned int issue_flags)
                req->flags &= ~REQ_F_HASH_LOCKED;
 
        ret = __io_arm_poll_handler(req, poll, &ipt, poll->events);
-       if (ret) {
+       if (ret > 0) {
                io_req_set_res(req, ipt.result_mask, 0);
                return IOU_OK;
        }
-       if (ipt.error) {
-               req_set_fail(req);
-               return ipt.error;
-       }
-
-       return IOU_ISSUE_SKIP_COMPLETE;
+       return ret ?: IOU_ISSUE_SKIP_COMPLETE;
 }
 
 int io_poll_remove(struct io_kiocb *req, unsigned int issue_flags)