io_uring/kbuf: use mmap_lock to sync with mmap

A preparation / cleanup patch simplifying the buf ring - mmap
synchronisation. Instead of relying on RCU, which is trickier, do it by
grabbing the mmap_lock when when anyone tries to publish or remove a
registered buffer to / from ->io_bl_xa.

Modifications of the xarray should always be protected by both
->uring_lock and ->mmap_lock, while lookups should hold either of them.
While a struct io_buffer_list is in the xarray, the mmap related fields
like ->flags and ->buf_pages should stay stable.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/af13bde56ee1a26bcaefaa9aad37a9ea318a590e.1732886067.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 0 insertions, 1 deletions

diff --git a/io_uring/kbuf.h b/io_uring/kbuf.h
index 36aadfe5ac00..d5e4afcbfbb3 100644
--- a/io_uring/kbuf.h
+++ b/io_uring/kbuf.h
@@ -25,7 +25,6 @@ struct io_buffer_list {
 			struct page **buf_pages;
 			struct io_uring_buf_ring *buf_ring;
 		};
-		struct rcu_head rcu;
 	};
 	__u16 bgid;