From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 33A5CCCA482 for ; Mon, 20 Jun 2022 14:01:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349034AbiFTOAz (ORCPT ); Mon, 20 Jun 2022 10:00:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44182 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351550AbiFTNy4 (ORCPT ); Mon, 20 Jun 2022 09:54:56 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4DC3233343; Mon, 20 Jun 2022 06:21:09 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 1BA3760FA2; Mon, 20 Jun 2022 13:20:54 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2C5FCC3411B; Mon, 20 Jun 2022 13:20:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1655731253; bh=yxrt/AhYhZ+ptvTBbqTsXTtDDwvi/BZIk1CzdojwcHk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=wSqmC3Zi1cHp3gOXWMFINbAOeJgacGQzyoqmknlUoKFTFXVFP0uFTLXuKKO+GL8fL YAALLqnP2CtE7oqlZYe3borjHOhsAtkCJ8/jU/10G8JvmMmdKqACrSBLzXIL5YVice 8H3os3aWKdyxGs3JAu4J+2cM759mpDGxUWsm+O3s= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Theodore Tso , Sultan Alsawaf , Dominik Brodowski , "Jason A. Donenfeld" Subject: [PATCH 5.4 160/240] random: use static branch for crng_ready() Date: Mon, 20 Jun 2022 14:51:01 +0200 Message-Id: <20220620124743.643795860@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220620124737.799371052@linuxfoundation.org> References: <20220620124737.799371052@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: "Jason A. Donenfeld" commit f5bda35fba615ace70a656d4700423fa6c9bebee upstream. Since crng_ready() is only false briefly during initialization and then forever after becomes true, we don't need to evaluate it after, making it a prime candidate for a static branch. One complication, however, is that it changes state in a particular call to credit_init_bits(), which might be made from atomic context, which means we must kick off a workqueue to change the static key. Further complicating things, credit_init_bits() may be called sufficiently early on in system initialization such that system_wq is NULL. Fortunately, there exists the nice function execute_in_process_context(), which will immediately execute the function if !in_interrupt(), and otherwise defer it to a workqueue. During early init, before workqueues are available, in_interrupt() is always false, because interrupts haven't even been enabled yet, which means the function in that case executes immediately. Later on, after workqueues are available, in_interrupt() might be true, but in that case, the work is queued in system_wq and all goes well. Cc: Theodore Ts'o Cc: Sultan Alsawaf Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld Signed-off-by: Greg Kroah-Hartman --- drivers/char/random.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -77,8 +77,9 @@ static enum { CRNG_EMPTY = 0, /* Little to no entropy collected */ CRNG_EARLY = 1, /* At least POOL_EARLY_BITS collected */ CRNG_READY = 2 /* Fully initialized with POOL_READY_BITS collected */ -} crng_init = CRNG_EMPTY; -#define crng_ready() (likely(crng_init >= CRNG_READY)) +} crng_init __read_mostly = CRNG_EMPTY; +static DEFINE_STATIC_KEY_FALSE(crng_is_ready); +#define crng_ready() (static_branch_likely(&crng_is_ready) || crng_init >= CRNG_READY) /* Various types of waiters for crng_init->CRNG_READY transition. */ static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait); static struct fasync_struct *fasync; @@ -108,6 +109,11 @@ bool rng_is_initialized(void) } EXPORT_SYMBOL(rng_is_initialized); +static void crng_set_ready(struct work_struct *work) +{ + static_branch_enable(&crng_is_ready); +} + /* Used by wait_for_random_bytes(), and considered an entropy collector, below. */ static void try_to_generate_entropy(void); @@ -267,7 +273,7 @@ static void crng_reseed(void) ++next_gen; WRITE_ONCE(base_crng.generation, next_gen); WRITE_ONCE(base_crng.birth, jiffies); - if (!crng_ready()) + if (!static_branch_likely(&crng_is_ready)) crng_init = CRNG_READY; spin_unlock_irqrestore(&base_crng.lock, flags); memzero_explicit(key, sizeof(key)); @@ -782,6 +788,7 @@ static void extract_entropy(void *buf, s static void credit_init_bits(size_t nbits) { + static struct execute_work set_ready; unsigned int new, orig, add; unsigned long flags; @@ -797,6 +804,7 @@ static void credit_init_bits(size_t nbit if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) { crng_reseed(); /* Sets crng_init to CRNG_READY under base_crng.lock. */ + execute_in_process_context(crng_set_ready, &set_ready); process_random_ready_list(); wake_up_interruptible(&crng_init_wait); kill_fasync(&fasync, SIGIO, POLL_IN); @@ -1306,7 +1314,7 @@ SYSCALL_DEFINE3(getrandom, char __user * if (count > INT_MAX) count = INT_MAX; - if (!(flags & GRND_INSECURE) && !crng_ready()) { + if (!crng_ready() && !(flags & GRND_INSECURE)) { int ret; if (flags & GRND_NONBLOCK)