lib/vsprintf: Remove static_branch_likely() from __ptr_to_hashval().

Sebastian Andrzej Siewior · pmladek · commit e4279b599863 · 2022-09-29T13:44:27.000+02:00
Using static_branch_likely() to signal that ptr_key has been filled is a bit much given that it is not a fast path. Replace static_branch_likely() with bool for condition and a memory barrier for ptr_key. Suggested-by: Petr Mladek <pmladek@suse.com> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Signed-off-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20220927104912.622645-2-bigeasy@linutronix.de
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
@@ -750,37 +750,34 @@ static int __init debug_boot_weak_hash_enable(char *str)
 }
 early_param("debug_boot_weak_hash", debug_boot_weak_hash_enable);
 
-static DEFINE_STATIC_KEY_FALSE(filled_random_ptr_key);
-
-static void enable_ptr_key_workfn(struct work_struct *work)
-{
-	static_branch_enable(&filled_random_ptr_key);
-}
+static bool filled_random_ptr_key __read_mostly;
 
 /* Maps a pointer to a 32 bit unique identifier. */
 static inline int __ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
 {
 	static siphash_key_t ptr_key __read_mostly;
 	unsigned long hashval;
 
-	if (!static_branch_likely(&filled_random_ptr_key)) {
+	if (!READ_ONCE(filled_random_ptr_key)) {
 		static bool filled = false;
 		static DEFINE_SPINLOCK(filling);
-		static DECLARE_WORK(enable_ptr_key_work, enable_ptr_key_workfn);
 		unsigned long flags;
 
-		if (!system_unbound_wq || !rng_is_initialized() ||
+		if (!rng_is_initialized() ||
 		    !spin_trylock_irqsave(&filling, flags))
 			return -EAGAIN;
 
 		if (!filled) {
 			get_random_bytes(&ptr_key, sizeof(ptr_key));
-			queue_work(system_unbound_wq, &enable_ptr_key_work);
+			/* Pairs with smp_rmb() before reading ptr_key. */
+			smp_wmb();
+			WRITE_ONCE(filled_random_ptr_key, true);
 			filled = true;
 		}
 		spin_unlock_irqrestore(&filling, flags);
 	}
-
+	/* Pairs with smp_wmb() after writing ptr_key. */
+	smp_rmb();
 
 #ifdef CONFIG_64BIT
 	hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key);
