io_uring: fix false positive KASAN warnings

io_req_local_work_add() peeks into the work list, which can be executed
in the meanwhile. It's completely fine without KASAN as we're in an RCU
read section and it's SLAB_TYPESAFE_BY_RCU. With KASAN though it may
trigger a false positive warning because internal io_uring caches are
sanitised.

Remove sanitisation from the io_uring request cache for now.

Cc: stable@vger.kernel.org
Fixes: 8751d154 ("io_uring: reduce scheduling due to tw")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/c6fbf7a82a341e66a0007c76eefd9d57f2d3ba51.1691541473.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/io_uring.c

@@ -229,7 +229,6 @@ static inline void req_fail_link_node(struct io_kiocb *req, int res)
 static inline void io_req_add_to_cache(struct io_kiocb *req, struct io_ring_ctx *ctx)
 {
 	wq_stack_add_head(&req->comp_list, &ctx->submit_state.free_list);
-	kasan_poison_object_data(req_cachep, req);
 }
 
 static __cold void io_ring_ctx_ref_free(struct percpu_ref *ref)

io_uring/io_uring.h

@@ -354,7 +354,6 @@ static inline struct io_kiocb *io_extract_req(struct io_ring_ctx *ctx)
 	struct io_kiocb *req;
 
 	req = container_of(ctx->submit_state.free_list.next, struct io_kiocb, comp_list);
-	kasan_unpoison_object_data(req_cachep, req);
 	wq_stack_extract(&ctx->submit_state.free_list);
 	return req;
 }