task_stack.h: clean-up stack_not_used() implementation

Inside the small stack_not_used() function there are several ifdefs for
stack growing-up vs.  regular versions.  Instead just implement this
function two times, one for growing-up and another regular.

Add comments like /* !CONFIG_DEBUG_STACK_USAGE */ to clarify what the
ifdefs are doing.

[linus.walleij@linaro.org: rebased, function moved elsewhere in the kernel]
Link: https://lkml.kernel.org/r/20250829-fork-cleanups-for-dynstack-v1-2-3bbaadce1f00@linaro.org
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Link: https://lore.kernel.org/20240311164638.2015063-13-pasha.tatashin@soleen.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Ben Segall <bsegall@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Mel Gorman <mgorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/exit.c b/kernel/exit.c
index 343eb97543d568baeb23142edcc9050a8b8be8bf..9f74e8f1c431b6aa6e391ff71aadf9895a3857ae 100644 (file)
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -780,24 +780,29 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
 }
 
 #ifdef CONFIG_DEBUG_STACK_USAGE
+#ifdef CONFIG_STACK_GROWSUP
 unsigned long stack_not_used(struct task_struct *p)
 {
        unsigned long *n = end_of_stack(p);
 
        do {    /* Skip over canary */
-# ifdef CONFIG_STACK_GROWSUP
                n--;
-# else
-               n++;
-# endif
        } while (!*n);
 
-# ifdef CONFIG_STACK_GROWSUP
        return (unsigned long)end_of_stack(p) - (unsigned long)n;
-# else
+}
+#else /* !CONFIG_STACK_GROWSUP */
+unsigned long stack_not_used(struct task_struct *p)
+{
+       unsigned long *n = end_of_stack(p);
+
+       do {    /* Skip over canary */
+               n++;
+       } while (!*n);
+
        return (unsigned long)n - (unsigned long)end_of_stack(p);
-# endif
 }
+#endif /* CONFIG_STACK_GROWSUP */
 
 /* Count the maximum pages reached in kernel stacks */
 static inline void kstack_histogram(unsigned long used_stack)
@@ -856,9 +861,9 @@ static void check_stack_usage(void)
        }
        spin_unlock(&low_water_lock);
 }
-#else
+#else /* !CONFIG_DEBUG_STACK_USAGE */
 static inline void check_stack_usage(void) {}
-#endif
+#endif /* CONFIG_DEBUG_STACK_USAGE */
 
 static void synchronize_group_exit(struct task_struct *tsk, long code)
 {