kdb: Remove unused flags stack

kdb_restore_flags() and kdb_save_flags() were added in 2010 by
commit 5d5314d ("kdb: core for kgdb back end (1 of 2)")
but have remained unused.

Remove them, and their associated storage.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20250112012049.319515-1-linux@treblig.org
Signed-off-by: Daniel Thompson (RISCstar) <danielt@kernel.org>

include/linux/kdb.h

@@ -140,9 +140,6 @@ extern const char *kdb_diemsg;
 
 extern unsigned int kdb_flags;	/* Global flags, see kdb_state for per cpu state */
 
-extern void kdb_save_flags(void);
-extern void kdb_restore_flags(void);
-
 #define KDB_FLAG(flag)		(kdb_flags & KDB_FLAG_##flag)
 #define KDB_FLAG_SET(flag)	((void)(kdb_flags |= KDB_FLAG_##flag))
 #define KDB_FLAG_CLEAR(flag)	((void)(kdb_flags &= ~KDB_FLAG_##flag))

kernel/debug/kdb/kdb_support.c

@@ -536,21 +536,3 @@ bool kdb_task_state(const struct task_struct *p, const char *mask)
 
 	return strchr(mask, state);
 }
-
-/* Maintain a small stack of kdb_flags to allow recursion without disturbing
- * the global kdb state.
- */
-
-static int kdb_flags_stack[4], kdb_flags_index;
-
-void kdb_save_flags(void)
-{
-	BUG_ON(kdb_flags_index >= ARRAY_SIZE(kdb_flags_stack));
-	kdb_flags_stack[kdb_flags_index++] = kdb_flags;
-}
-
-void kdb_restore_flags(void)
-{
-	BUG_ON(kdb_flags_index <= 0);
-	kdb_flags = kdb_flags_stack[--kdb_flags_index];
-}