[PATCH] sched: dynamic: Fix preemption model strings

[Mark Rutland <mark.rutland@arm.com>]

We recently removed the enum values 'preempt_dynamic_none' and
'preempt_dynamic_voluntary', but forgot to update preempt_modes[]
accordingly. Due to this, preempt_model_str() and sched_dynamic_show()
produce incorrect output, with the wrong preemption model string in
backtraces, and empty output for /sys/kernel/debug/sched/preempt.

Update preempt_modes[] to account for the removed enum values. Given
that CONFIG_PREEMPT_DYNAMIC now depends on CONFIG_ARCH_HAS_PREEMPT_LAZY,
and given that only 'preempt_dynamic_full' and 'preempt_dynamic_lazy'
remain, sched_dynamic_show() no longer needs to skip any model strings.

Reported-by: Jinjie Ruan <ruanjinjie@huawei.com>
Fixes: 9650ce11f2e3 ("sched: dynamic: Simplify preempt model accessors")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Mete Durlu <meted@linux.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
---
 kernel/sched/core.c  |  2 +-
 kernel/sched/debug.c | 10 ++--------
 2 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 545f49491bcde..5a61650f12b7d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7960,7 +7960,7 @@ static inline void preempt_dynamic_init(void) { }
 #endif /* CONFIG_PREEMPT_DYNAMIC */
 
 const char *preempt_modes[] = {
-	"none", "voluntary", "full", "lazy", NULL,
+	"full", "lazy", NULL,
 };
 
 const char *preempt_model_str(void)
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 9883e4c4976bf..fda10b3fa249a 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -280,16 +280,10 @@ static ssize_t sched_dynamic_write(struct file *filp, const char __user *ubuf,
 
 static int sched_dynamic_show(struct seq_file *m, void *v)
 {
-	int i = (IS_ENABLED(CONFIG_PREEMPT_RT) || IS_ENABLED(CONFIG_ARCH_HAS_PREEMPT_LAZY)) * 2;
 	int mode = READ_ONCE(preempt_dynamic_mode);
-	int j;
 
-	/* Count entries in NULL terminated preempt_modes */
-	for (j = 0; preempt_modes[j]; j++)
-		;
-	j -= !IS_ENABLED(CONFIG_ARCH_HAS_PREEMPT_LAZY);
-
-	for (; i < j; i++) {
+	/* Stop at NULL terminator */
+	for (int i = 0; preempt_modes[i]; i++) {
 		if (mode == i)
 			seq_puts(m, "(");
 		seq_puts(m, preempt_modes[i]);
-- 
2.30.2