procfs: Use generic_file_llseek in /proc/kcore

/proc/kcore has no llseek and then falls down to use default_llseek.
This is racy against read_kcore() that directly manipulates fpos
but it doesn't hold the bkl there so using it in llseek doesn't
protect anything.

Let's use generic_file_llseek() instead.

Signed-off-by: Frederic Weisbecker <[email protected]>
Acked-by: Arnd Bergmann <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: John Kacur <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: Al Viro <[email protected]>

fs/proc/kcore.c

@@ -557,6 +557,7 @@ static int open_kcore(struct inode *inode, struct file *filp)
 static const struct file_operations proc_kcore_operations = {
 	.read		= read_kcore,
 	.open		= open_kcore,
+	.llseek		= generic_file_llseek,
 };
 
 #ifdef CONFIG_MEMORY_HOTPLUG