UPSTREAM: io_uring/poll: serialize poll linked timer start with poll removal

Commit ef7dfac5 upstream.

We selectively grab the ctx->uring_lock for poll update/removal, but
we really should grab it from the start to fully synchronize with
linked timeouts. Normally this is indeed the case, but if requests
are forced async by the application, we don't fully cover removal
and timer disarm within the uring_lock.

Make this simpler by having consistent locking state for poll removal.

Bug: 290270326
Cc: stable@vger.kernel.org # 6.1+
Reported-by: Querijn Voet <querijnqyn@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 24f47376)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I6632b7d78493b0dfc0fb26204d34823045c03f72