If we get woken spuriously when polling and fail the operation with
-EAGAIN again, then we generally only allow polling again if data
had been transferred at some point. This is indicated with
REQ_F_PARTIAL_IO. However, if the spurious poll triggers when the socket
was originally empty, then we haven't transferred data yet and we will
fail the poll re-arm. This either punts the socket to io-wq if it's
blocking, or it fails the request with -EAGAIN if not. Neither condition
is desirable, as the former will slow things down, while the latter
will make the application confused.

We want to ensure that a repeated poll trigger doesn't lead to infinite
work making no progress, that's what the REQ_F_PARTIAL_IO check was
for. But it doesn't protect against a loop post the first receive, and
it's unnecessarily strict if we started out with an empty socket.

Add a somewhat random retry count, just to put an upper limit on the
potential number of retries that will be done. This should be high enough
that we won't really hit it in practice, unless something needs to be
aborted anyway.

Cc: stable@vger.kernel.org # v5.10+
Link: https://github.com/axboe/liburing/issues/364


Signed-off-by: Jens Axboe <axboe@kernel.dk>

In preparation for adding limits, and one more user, abstract out the
core bits of the allocation+free cache.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

This is where it's used, move the flush handler in there.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

Commit 3a3d47fa9cfd ("io_uring: make io_uring_types.h public") moved
a bunch of io_uring types to a kernel wide header, so we could make
tracing a bit saner rather than pass in a ton of arguments.

However, there are a few types in there that are not really needed to
be system wide. Move the cancel data and mapped buffers back to the
appropriate io_uring local headers.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

Poll cancellation will be soon need to grab ->uring_lock inside, pass
the locking state, i.e. issue_flags, inside the cancellation functions.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/b86781d047727c07163443b57551a3fa57c7c5e1.1655371007.git.asml.silence@gmail.com


Reviewed-by: Hao Xu <howeyxu@tencent.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Add a io_poll_issue() rather than export the general task_work locking
and io_issue_sqe(), and put the io_op_defs definition and structure into
a separate header file so that poll can use it.

Signed-off-by: Jens Axboe <axboe@kernel.dk>