[PATCH 1/3] jump_label: Pull get_online_cpus() into generic code

[Peter Zijlstra]

This change does two things; it moves the get_online_cpus() call into
generic code, with the aim of later providing some static_key ops that
avoid it.

And as a side effect it inverts the relation between cpu_hotplug_lock
and jump_label_mutex.

Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
--- a/arch/mips/kernel/jump_label.c
+++ b/arch/mips/kernel/jump_label.c
@@ -58,7 +58,6 @@ void arch_jump_label_transform(struct ju
                insn.word = 0; /* nop */
        }
 
-       get_online_cpus();
        mutex_lock(&text_mutex);
        if (IS_ENABLED(CONFIG_CPU_MICROMIPS)) {
                insn_p->halfword[0] = insn.word >> 16;
@@ -70,7 +69,6 @@ void arch_jump_label_transform(struct ju
                           (unsigned long)insn_p + sizeof(*insn_p));
 
        mutex_unlock(&text_mutex);
-       put_online_cpus();
 }
 
 #endif /* HAVE_JUMP_LABEL */
--- a/arch/sparc/kernel/jump_label.c
+++ b/arch/sparc/kernel/jump_label.c
@@ -41,12 +41,10 @@ void arch_jump_label_transform(struct ju
                val = 0x01000000;
        }
 
-       get_online_cpus();
        mutex_lock(&text_mutex);
        *insn = val;
        flushi(insn);
        mutex_unlock(&text_mutex);
-       put_online_cpus();
 }
 
 #endif
--- a/arch/tile/kernel/jump_label.c
+++ b/arch/tile/kernel/jump_label.c
@@ -45,14 +45,12 @@ static void __jump_label_transform(struc
 void arch_jump_label_transform(struct jump_entry *e,
                                enum jump_label_type type)
 {
-       get_online_cpus();
        mutex_lock(&text_mutex);
 
        __jump_label_transform(e, type);
        flush_icache_range(e->code, e->code + sizeof(tilegx_bundle_bits));
 
        mutex_unlock(&text_mutex);
-       put_online_cpus();
 }
 
 __init_or_module void arch_jump_label_transform_static(struct jump_entry *e,
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -105,11 +105,9 @@ static void __jump_label_transform(struc
 void arch_jump_label_transform(struct jump_entry *entry,
                               enum jump_label_type type)
 {
-       get_online_cpus();
        mutex_lock(&text_mutex);
        __jump_label_transform(entry, type, NULL, 0);
        mutex_unlock(&text_mutex);
-       put_online_cpus();
 }
 
 static enum {
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -15,6 +15,7 @@
 #include <linux/static_key.h>
 #include <linux/jump_label_ratelimit.h>
 #include <linux/bug.h>
+#include <linux/cpu.h>
 
 #ifdef HAVE_JUMP_LABEL
 
@@ -124,6 +125,12 @@ void static_key_slow_inc(struct static_k
                        return;
        }
 
+       /*
+        * A number of architectures need to synchronize I$ across
+        * the all CPUs, for that to be serialized against CPU hot-plug
+        * we need to avoid CPUs coming online.
+        */
+       get_online_cpus();
        jump_label_lock();
        if (atomic_read(&key->enabled) == 0) {
                atomic_set(&key->enabled, -1);
@@ -133,6 +140,7 @@ void static_key_slow_inc(struct static_k
                atomic_inc(&key->enabled);
        }
        jump_label_unlock();
+       put_online_cpus();
 }
 EXPORT_SYMBOL_GPL(static_key_slow_inc);
 
@@ -146,6 +154,7 @@ static void __static_key_slow_dec(struct
         * returns is unbalanced, because all other static_key_slow_inc()
         * instances block while the update is in progress.
         */
+       get_online_cpus();
        if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
                WARN(atomic_read(&key->enabled) < 0,
                     "jump label: negative count!\n");
@@ -159,6 +168,7 @@ static void __static_key_slow_dec(struct
                jump_label_update(key);
        }
        jump_label_unlock();
+       put_online_cpus();
 }
 
 static void jump_label_update_timeout(struct work_struct *work)
@@ -592,6 +602,10 @@ jump_label_module_notify(struct notifier
 
        switch (val) {
        case MODULE_STATE_COMING:
+               /*
+                * XXX do we need get_online_cpus() ?  the module isn't
+                * executable yet, so nothing should be looking at our code.
+                */
                jump_label_lock();
                ret = jump_label_add_module(mod);
                if (ret) {