locking/static_key: Factor out the fast path of static_key_slow_dec()

static_key_slow_dec() checks if the atomic enable count is larger
than 1, and if so there decrements it before taking the jump_label_lock.
Move this logic into a helper for reuse in rate limitted keys.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: alexei.starovoitov@gmail.com
Cc: ard.biesheuvel@linaro.org
Cc: oss-drivers@netronome.com
Cc: yamada.masahiro@socionext.com
Link: https://lkml.kernel.org/r/20190330000854.30142-3-jakub.kicinski@netronome.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 73bbbad..02c3d11 100644 (file)
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -202,13 +202,13 @@ void static_key_disable(struct static_key *key)
 }
 EXPORT_SYMBOL_GPL(static_key_disable);
 
-static void __static_key_slow_dec_cpuslocked(struct static_key *key,
-                                          unsigned long rate_limit,
-                                          struct delayed_work *work)
+static bool static_key_slow_try_dec(struct static_key *key)
 {
        int val;
 
-       lockdep_assert_cpus_held();
+       val = atomic_fetch_add_unless(&key->enabled, -1, 1);
+       if (val == 1)
+               return false;
 
        /*
         * The negative count check is valid even when a negative
@@ -217,11 +217,18 @@ static void __static_key_slow_dec_cpuslocked(struct static_key *key,
         * returns is unbalanced, because all other static_key_slow_inc()
         * instances block while the update is in progress.
         */
-       val = atomic_fetch_add_unless(&key->enabled, -1, 1);
-       if (val != 1) {
-               WARN(val < 0, "jump label: negative count!\n");
+       WARN(val < 0, "jump label: negative count!\n");
+       return true;
+}
+
+static void __static_key_slow_dec_cpuslocked(struct static_key *key,
+                                          unsigned long rate_limit,
+                                          struct delayed_work *work)
+{
+       lockdep_assert_cpus_held();
+
+       if (static_key_slow_try_dec(key))
                return;
-       }
 
        jump_label_lock();
        if (atomic_dec_and_test(&key->enabled)) {