sched: Use {READ,WRITE}_ONCE() for preempt_dynamic_mode

Robots figured out you can read and write this concurrently and got
'upset'. Gemini even noted sched_dynamic_show() can generate
'confusing' output if it observed different values during the
printing.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260511120627.176946327@infradead.org

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b3a416b1c251001335aa77b3afde7b52fe21431c..83202f090f0c45dd5167ae57f5d0343510ec9cc9 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7979,7 +7979,7 @@ static void __sched_dynamic_update(int mode)
                break;
        }
 
-       preempt_dynamic_mode = mode;
+       WRITE_ONCE(preempt_dynamic_mode, mode);
 }
 
 void sched_dynamic_update(int mode)
@@ -8020,12 +8020,13 @@ static void __init preempt_dynamic_init(void)
        }
 }
 
-# define PREEMPT_MODEL_ACCESSOR(mode) \
-       bool preempt_model_##mode(void)                                          \
-       {                                                                        \
-               WARN_ON_ONCE(preempt_dynamic_mode == preempt_dynamic_undefined); \
-               return preempt_dynamic_mode == preempt_dynamic_##mode;           \
-       }                                                                        \
+# define PREEMPT_MODEL_ACCESSOR(mode)                                  \
+       bool preempt_model_##mode(void)                                 \
+       {                                                               \
+               int mode = READ_ONCE(preempt_dynamic_mode);             \
+               WARN_ON_ONCE(mode == preempt_dynamic_undefined);        \
+               return mode == preempt_dynamic_##mode;                  \
+       }                                                               \
        EXPORT_SYMBOL_GPL(preempt_model_##mode)
 
 PREEMPT_MODEL_ACCESSOR(none);

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index af13a896858c5ea324ed7fa5135f027317506e95..4cdf2f9c5d9ef0726640b2b7b2202b94252552a4 100644 (file)
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -281,6 +281,7 @@ 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 */
@@ -289,10 +290,10 @@ static int sched_dynamic_show(struct seq_file *m, void *v)
        j -= !IS_ENABLED(CONFIG_ARCH_HAS_PREEMPT_LAZY);
 
        for (; i < j; i++) {
-               if (preempt_dynamic_mode == i)
+               if (mode == i)
                        seq_puts(m, "(");
                seq_puts(m, preempt_modes[i]);
-               if (preempt_dynamic_mode == i)
+               if (mode == i)
                        seq_puts(m, ")");
 
                seq_puts(m, " ");