Merge tag 'io_uring-6.12-20241018' of git://git.kernel.dk/linux

Pull io_uring fixes from Jens Axboe:

 - Fix a regression this merge window where cloning of registered
   buffers didn't take into account the dummy_ubuf

 - Fix a race with reading how many SQRING entries are available,
   causing userspace to need to loop around io_uring_sqring_wait()
   rather than being able to rely on SQEs being available when it
   returned

 - Ensure that the SQPOLL thread is TASK_RUNNING before running
   task_work off the cancelation exit path

* tag 'io_uring-6.12-20241018' of git://git.kernel.dk/linux:
  io_uring/sqpoll: ensure task state is TASK_RUNNING when running task_work
  io_uring/rsrc: ignore dummy_ubuf for buffer cloning
  io_uring/sqpoll: close race on waiting for sqring entries

Author: torvalds

io_uring/io_uring.h

@@ -284,7 +284,14 @@ static inline bool io_sqring_full(struct io_ring_ctx *ctx)
 {
 	struct io_rings *r = ctx->rings;
 
-	return READ_ONCE(r->sq.tail) - ctx->cached_sq_head == ctx->sq_entries;
+	/*
+	 * SQPOLL must use the actual sqring head, as using the cached_sq_head
+	 * is race prone if the SQPOLL thread has grabbed entries but not yet
+	 * committed them to the ring. For !SQPOLL, this doesn't matter, but
+	 * since this helper is just used for SQPOLL sqring waits (or POLLOUT),
+	 * just read the actual sqring head unconditionally.
+	 */
+	return READ_ONCE(r->sq.tail) - READ_ONCE(r->sq.head) == ctx->sq_entries;
 }
 
 static inline unsigned int io_sqring_entries(struct io_ring_ctx *ctx)
@@ -320,6 +327,7 @@ static inline int io_run_task_work(void)
 		if (current->io_uring) {
 			unsigned int count = 0;
 
+			__set_current_state(TASK_RUNNING);
 			tctx_task_work_run(current->io_uring, UINT_MAX, &count);
 			if (count)
 				ret = true;

io_uring/rsrc.c

@@ -1176,7 +1176,8 @@ static int io_clone_buffers(struct io_ring_ctx *ctx, struct io_ring_ctx *src_ctx
 	for (i = 0; i < nbufs; i++) {
 		struct io_mapped_ubuf *src = src_ctx->user_bufs[i];
 
-		refcount_inc(&src->refs);
+		if (src != &dummy_ubuf)
+			refcount_inc(&src->refs);
 		user_bufs[i] = src;
 	}