[PATCH v4 1/2] fs/aio: Restrict kiocb_set_cancel_fn() to I/O submitted via libaio

[Bart Van Assche <bvanassche@acm.org>]

If kiocb_set_cancel_fn() is called for I/O submitted via io_uring, the
following kernel warning appears:

WARNING: CPU: 3 PID: 368 at fs/aio.c:598 kiocb_set_cancel_fn+0x9c/0xa8
Call trace:
 kiocb_set_cancel_fn+0x9c/0xa8
 ffs_epfile_read_iter+0x144/0x1d0
 io_read+0x19c/0x498
 io_issue_sqe+0x118/0x27c
 io_submit_sqes+0x25c/0x5fc
 __arm64_sys_io_uring_enter+0x104/0xab0
 invoke_syscall+0x58/0x11c
 el0_svc_common+0xb4/0xf4
 do_el0_svc+0x2c/0xb0
 el0_svc+0x2c/0xa4
 el0t_64_sync_handler+0x68/0xb4
 el0t_64_sync+0x1a4/0x1a8

Fix this by setting the IOCB_AIO_RW flag for read and write I/O that is
submitted by libaio.

Suggested-by: Jens Axboe <axboe@kernel.dk>
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>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 fs/aio.c           | 9 ++++++++-
 include/linux/fs.h | 2 ++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/aio.c b/fs/aio.c
index bb2ff48991f3..da18dbcfcb22 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -593,6 +593,13 @@ void kiocb_set_cancel_fn(struct kiocb *iocb, kiocb_cancel_fn *cancel)
 	struct kioctx *ctx = req->ki_ctx;
 	unsigned long flags;
 
+	/*
+	 * kiocb didn't come from aio or is neither a read nor a write, hence
+	 * ignore it.
+	 */
+	if (!(iocb->ki_flags & IOCB_AIO_RW))
+		return;
+
 	if (WARN_ON_ONCE(!list_empty(&req->ki_list)))
 		return;
 
@@ -1509,7 +1516,7 @@ static int aio_prep_rw(struct kiocb *req, const struct iocb *iocb)
 	req->ki_complete = aio_complete_rw;
 	req->private = NULL;
 	req->ki_pos = iocb->aio_offset;
-	req->ki_flags = req->ki_filp->f_iocb_flags;
+	req->ki_flags = req->ki_filp->f_iocb_flags | IOCB_AIO_RW;
 	if (iocb->aio_flags & IOCB_FLAG_RESFD)
 		req->ki_flags |= IOCB_EVENTFD;
 	if (iocb->aio_flags & IOCB_FLAG_IOPRIO) {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c9deac59c29a..d47306fe1121 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -352,6 +352,8 @@ enum rw_hint {
  * unrelated IO (like cache flushing, new IO generation, etc).
  */
 #define IOCB_DIO_CALLER_COMP	(1 << 22)
+/* kiocb is a read or write operation submitted by fs/aio.c. */
+#define IOCB_AIO_RW		(1 << 23)
 
 /* for use in trace events */
 #define TRACE_IOCB_STRINGS \