sysfs: upgrade OOB write by buggy .show hook into WARNing

[Alexey Dobriyan <adobriyan@gmail.com>]

Buggy .show hook will get just 1 line of dmesg:

	fill_read_buffer: ext4_attr_show+0x0/0x600 returned bad count

It may or may not oops later in some unrelated process.

But buggy .show hook most likely is corrupting random memory past sysfs
buffer therefore deserving more. WARN, make it more visible and let
QA machines panic earlier.

Also, delete useless cast -- "count" is >=0 at this point.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 fs/sysfs/file.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -70,9 +70,8 @@ static int sysfs_kf_seq_show(struct seq_file *sf, void *v)
 	 * The code works fine with PAGE_SIZE return but it's likely to
 	 * indicate truncated result or overflow in normal use cases.
 	 */
-	if (count >= (ssize_t)PAGE_SIZE) {
-		printk("fill_read_buffer: %pS returned bad count\n",
-				ops->show);
+	if (count >= PAGE_SIZE) {
+		WARN(1, "OOB write or bad count %zd at %pS\n", count, ops->show);
 		/* Try to struggle along */
 		count = PAGE_SIZE - 1;
 	}