[PATCH] crypto: avoid unnecessary work when self-tests are disabled

[Eric Biggers <ebiggers@kernel.org>]

From: Eric Biggers <ebiggers@google.com>

Currently, registering an algorithm with the crypto API always causes a
notification to be posted to the "cryptomgr", which then creates a
kthread to self-test the algorithm.  However, if self-tests are disabled
in the kconfig (as is the default option), then this kthread just
notifies waiters that the algorithm has been tested, then exits.

This causes a significant amount of overhead, especially in the kthread
creation and destruction, which is not necessary at all.  For example,
in a quick test I found that booting a "minimum" x86_64 kernel with all
the crypto options enabled (except for the self-tests) takes about 400ms
until PID 1 can start.  Of that, a full 13ms is spent just doing this
pointless dance, involving a kthread being created, run, and destroyed
over 200 times.  That's over 3% of the entire kernel start time.

Fix this by just skipping the creation of the test larval and the
posting of the registration notification entirely, when self-tests are
disabled.  Also compile out the unnecessary code in algboss.c.

While this patch is an optimization and not a "fix" per se, I've marked
it as for stable, due to the large improvement it can make to boot time.

Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 crypto/algapi.c  |  3 ++-
 crypto/algboss.c | 11 +++++++----
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/crypto/algapi.c b/crypto/algapi.c
index 5c69ff8e8fa5c..018935cb8417d 100644
--- a/crypto/algapi.c
+++ b/crypto/algapi.c
@@ -226,7 +226,8 @@ static struct crypto_larval *crypto_alloc_test_larval(struct crypto_alg *alg)
 {
 	struct crypto_larval *larval;
 
-	if (!IS_ENABLED(CONFIG_CRYPTO_MANAGER))
+	if (!IS_ENABLED(CONFIG_CRYPTO_MANAGER) ||
+	    IS_ENABLED(CONFIG_CRYPTO_MANAGER_DISABLE_TESTS))
 		return NULL;
 
 	larval = crypto_larval_alloc(alg->cra_name,
diff --git a/crypto/algboss.c b/crypto/algboss.c
index eb5fe84efb83e..e6f0443d08048 100644
--- a/crypto/algboss.c
+++ b/crypto/algboss.c
@@ -171,16 +171,18 @@ static int cryptomgr_schedule_probe(struct crypto_larval *larval)
 	return NOTIFY_OK;
 }
 
+#ifdef CONFIG_CRYPTO_MANAGER_DISABLE_TESTS
+static int cryptomgr_schedule_test(struct crypto_alg *alg)
+{
+	return 0;
+}
+#else
 static int cryptomgr_test(void *data)
 {
 	struct crypto_test_param *param = data;
 	u32 type = param->type;
 	int err = 0;
 
-#ifdef CONFIG_CRYPTO_MANAGER_DISABLE_TESTS
-	goto skiptest;
-#endif
-
 	if (type & CRYPTO_ALG_TESTED)
 		goto skiptest;
 
@@ -229,6 +231,7 @@ static int cryptomgr_schedule_test(struct crypto_alg *alg)
 err:
 	return NOTIFY_OK;
 }
+#endif /* !CONFIG_CRYPTO_MANAGER_DISABLE_TESTS */
 
 static int cryptomgr_notify(struct notifier_block *this, unsigned long msg,
 			    void *data)

base-commit: f67dd6ce0723ad013395f20a3f79d8a437d3f455
-- 
2.38.1