UPSTREAM: io_uring: mem-account pbuf buckets

commit cc18cc5e upstream.

Potentially, someone may create as many pbuf bucket as there are indexes
in an xarray without any other restrictions bounding our memory usage,
put memory needed for the buckets under memory accounting.

Cc: <stable@vger.kernel.org>
Change-Id: Ifa28c35ec2058418c95356f26303db886d376fc5
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/d34c452e45793e978d26e2606211ec9070d329ea.1659622312.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit fa304068)
Bug: 268174392
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>