posix-timers: Initialize cache early and move pointer into __timer_data

Move posix_timers_cache initialization to posixtimer_init(). At that point
the memory subsystem is already up and running.

Also move the cache pointer to the __timer_data variable to avoid
potential false sharing, since it never was marked as __ro_after_init.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250402133114.253901-1-edumazet@google.com

Author: edumazet

kernel/time/posix-timers.c

@@ -30,8 +30,6 @@
 #include "timekeeping.h"
 #include "posix-timers.h"
 
-static struct kmem_cache *posix_timers_cache;
-
 /*
  * Timers are managed in a hash table for lockless lookup. The hash key is
  * constructed from current::signal and the timer ID and the timer is
@@ -49,10 +47,12 @@ struct timer_hash_bucket {
 static struct {
 	struct timer_hash_bucket	*buckets;
 	unsigned long			mask;
-} __timer_data __ro_after_init __aligned(2*sizeof(long));
+	struct kmem_cache		*cache;
+} __timer_data __ro_after_init __aligned(4*sizeof(long));
 
-#define timer_buckets	(__timer_data.buckets)
-#define timer_hashmask	(__timer_data.mask)
+#define timer_buckets		(__timer_data.buckets)
+#define timer_hashmask		(__timer_data.mask)
+#define posix_timers_cache	(__timer_data.cache)
 
 static const struct k_clock * const posix_clocks[];
 static const struct k_clock *clockid_to_kclock(const clockid_t id);
@@ -283,14 +283,6 @@ static int posix_get_hrtimer_res(clockid_t which_clock, struct timespec64 *tp)
 	return 0;
 }
 
-static __init int init_posix_timers(void)
-{
-	posix_timers_cache = kmem_cache_create("posix_timers_cache", sizeof(struct k_itimer),
-					       __alignof__(struct k_itimer), SLAB_ACCOUNT, NULL);
-	return 0;
-}
-__initcall(init_posix_timers);
-
 /*
  * The siginfo si_overrun field and the return value of timer_getoverrun(2)
  * are of type int. Clamp the overrun value to INT_MAX
@@ -1556,6 +1548,11 @@ static int __init posixtimer_init(void)
 	unsigned long i, size;
 	unsigned int shift;
 
+	posix_timers_cache = kmem_cache_create("posix_timers_cache",
+					       sizeof(struct k_itimer),
+					       __alignof__(struct k_itimer),
+					       SLAB_ACCOUNT, NULL);
+
 	if (IS_ENABLED(CONFIG_BASE_SMALL))
 		size = 512;
 	else