Revert "fs/aio: Make io_cancel() generate completions again"

Patch "fs/aio: Make io_cancel() generate completions again" is based on the
assumption that calling kiocb->ki_cancel() does not complete R/W requests.
This is incorrect: the two drivers that call kiocb_set_cancel_fn() callers
set a cancellation function that calls usb_ep_dequeue(). According to its
documentation, usb_ep_dequeue() calls the completion routine with status
-ECONNRESET. Hence this revert.

Cc: Benjamin LaHaise <ben@communityfibre.ca>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Avi Kivity <avi@scylladb.com>
Cc: Sandeep Dhavale <dhavale@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: stable@vger.kernel.org
Reported-by: syzbot+b91eb2ed18f599dd3c31@syzkaller.appspotmail.com
Fixes: 54cbc05 ("fs/aio: Make io_cancel() generate completions again")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20240304182945.3646109-1-bvanassche@acm.org
Acked-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: bvanassche

fs/aio.c

@@ -2165,11 +2165,14 @@ COMPAT_SYSCALL_DEFINE3(io_submit, compat_aio_context_t, ctx_id,
 #endif
 
 /* sys_io_cancel:
- *	Attempts to cancel an iocb previously passed to io_submit(). If the
- *	operation is successfully cancelled 0 is returned. May fail with
- *	-EFAULT if any of the data structures pointed to are invalid. May
- *	fail with -EINVAL if aio_context specified by ctx_id is invalid. Will
- *	fail with -ENOSYS if not implemented.
+ *	Attempts to cancel an iocb previously passed to io_submit.  If
+ *	the operation is successfully cancelled, the resulting event is
+ *	copied into the memory pointed to by result without being placed
+ *	into the completion queue and 0 is returned.  May fail with
+ *	-EFAULT if any of the data structures pointed to are invalid.
+ *	May fail with -EINVAL if aio_context specified by ctx_id is
+ *	invalid.  May fail with -EAGAIN if the iocb specified was not
+ *	cancelled.  Will fail with -ENOSYS if not implemented.
  */
 SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
 		struct io_event __user *, result)
@@ -2200,12 +2203,14 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
 	}
 	spin_unlock_irq(&ctx->ctx_lock);
 
-	/*
-	 * The result argument is no longer used - the io_event is always
-	 * delivered via the ring buffer.
-	 */
-	if (ret == 0 && kiocb->rw.ki_flags & IOCB_AIO_RW)
-		aio_complete_rw(&kiocb->rw, -EINTR);
+	if (!ret) {
+		/*
+		 * The result argument is no longer used - the io_event is
+		 * always delivered via the ring buffer. -EINPROGRESS indicates
+		 * cancellation is progress:
+		 */
+		ret = -EINPROGRESS;
+	}
 
 	percpu_ref_put(&ctx->users);