[PATCH 5.10 589/593] io_uring: fix blocking inline submission

[Greg Kroah-Hartman]

From: Pavel Begunkov <asml.silence@xxxxxxxxx>

commit 976517f162a05f4315b2373fd11585c395506259 upstream.

There is a complaint against sys_io_uring_enter() blocking if it submits
stdin reads. The problem is in __io_file_supports_async(), which
sees that it's a cdev and allows it to be processed inline.

Punt char devices using generic rules of io_file_supports_async(),
including checking for presence of *_iter() versions of rw callbacks.
Apparently, it will affect most of cdevs with some exceptions like
null and zero devices.

Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Birk Hirdman <lonjil@xxxxxxxxx>
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
Link: https://lore.kernel.org/r/d60270856b8a4560a639ef5f76e55eb563633599.1623236455.git.asml.silence@xxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/io_uring.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2770,7 +2770,7 @@ static bool io_file_supports_async(struc
 			return true;
 		return false;
 	}
-	if (S_ISCHR(mode) || S_ISSOCK(mode))
+	if (S_ISSOCK(mode))
 		return true;
 	if (S_ISREG(mode)) {
 		if (io_bdev_nowait(file->f_inode->i_sb->s_bdev) &&