bcachefs: ioctl: avoid stack overflow warning

Multiple ioctl handlers individually use a lot of stack space, and clang chooses
to inline them into the bch2_fs_ioctl() function, blowing through the warning
limit:

fs/bcachefs/chardev.c:655:6: error: stack frame size (1032) exceeds limit (1024) in 'bch2_fs_ioctl' [-Werror,-Wframe-larger-than]
  655 | long bch2_fs_ioctl(struct bch_fs *c, unsigned cmd, void __user *arg)

By marking the largest two of them as noinline_for_stack, no indidual code path
ends up using this much, which avoids the warning and reduces the possible
total stack usage in the ioctl handler.

Signed-off-by: Arnd Bergmann <[email protected]>
Signed-off-by: Kent Overstreet <[email protected]>

Author: arndb

fs/bcachefs/chardev.c

@@ -399,7 +399,7 @@ static long bch2_ioctl_data(struct bch_fs *c,
 	return ret;
 }
 
-static long bch2_ioctl_fs_usage(struct bch_fs *c,
+static noinline_for_stack long bch2_ioctl_fs_usage(struct bch_fs *c,
 				struct bch_ioctl_fs_usage __user *user_arg)
 {
 	struct bch_ioctl_fs_usage arg = {};
@@ -469,7 +469,7 @@ static long bch2_ioctl_query_accounting(struct bch_fs *c,
 }
 
 /* obsolete, didn't allow for new data types: */
-static long bch2_ioctl_dev_usage(struct bch_fs *c,
+static noinline_for_stack long bch2_ioctl_dev_usage(struct bch_fs *c,
 				 struct bch_ioctl_dev_usage __user *user_arg)
 {
 	struct bch_ioctl_dev_usage arg;