From patchwork Fri Oct 11 13:47:24 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Laurent Vivier X-Patchwork-Id: 11185525 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id EE6B714DB for ; Fri, 11 Oct 2019 13:47:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D8B0B206A1 for ; Fri, 11 Oct 2019 13:47:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728034AbfJKNr2 (ORCPT ); Fri, 11 Oct 2019 09:47:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37790 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727950AbfJKNr2 (ORCPT ); Fri, 11 Oct 2019 09:47:28 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E4EC510C0311; Fri, 11 Oct 2019 13:47:27 +0000 (UTC) Received: from thinkpad.redhat.com (ovpn-116-143.ams2.redhat.com [10.36.116.143]) by smtp.corp.redhat.com (Postfix) with ESMTP id B6248600C4; Fri, 11 Oct 2019 13:47:25 +0000 (UTC) From: Laurent Vivier To: linux-kernel@vger.kernel.org Cc: Matt Mackall , Herbert Xu , Marek Szyprowski , linux-crypto@vger.kernel.org, 'Linux Samsung SOC' , Laurent Vivier Subject: [PATCH v2] hwrng: core - move add_early_randomness() out of rng_mutex Date: Fri, 11 Oct 2019 15:47:24 +0200 Message-Id: <20191011134724.28651-1-lvivier@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.65]); Fri, 11 Oct 2019 13:47:28 +0000 (UTC) Sender: linux-samsung-soc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-samsung-soc@vger.kernel.org add_early_randomness() is called every time a new rng backend is added and every time it is set as the current rng provider. add_early_randomness() is called from functions locking rng_mutex, and if it hangs all the hw_random framework hangs: we can't read sysfs, add or remove a backend. This patch moves add_early_randomness() out of the rng_mutex zone. It only needs the reading_mutex. Signed-off-by: Laurent Vivier Reported-by: Marek Szyprowski Tested-by: Marek Szyprowski --- Notes: v2: in hwrng_register, take rng->ref only if rng is the new current_rng drivers/char/hw_random/core.c | 61 +++++++++++++++++++++++++---------- 1 file changed, 44 insertions(+), 17 deletions(-) diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index 80b850ef1bf6..d85c6e18a2d2 100644 --- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -112,6 +112,14 @@ static void drop_current_rng(void) } /* Returns ERR_PTR(), NULL or refcounted hwrng */ +static struct hwrng *get_current_rng_nolock(void) +{ + if (current_rng) + kref_get(¤t_rng->ref); + + return current_rng; +} + static struct hwrng *get_current_rng(void) { struct hwrng *rng; @@ -119,9 +127,7 @@ static struct hwrng *get_current_rng(void) if (mutex_lock_interruptible(&rng_mutex)) return ERR_PTR(-ERESTARTSYS); - rng = current_rng; - if (rng) - kref_get(&rng->ref); + rng = get_current_rng_nolock(); mutex_unlock(&rng_mutex); return rng; @@ -156,8 +162,6 @@ static int hwrng_init(struct hwrng *rng) reinit_completion(&rng->cleanup_done); skip_init: - add_early_randomness(rng); - current_quality = rng->quality ? : default_quality; if (current_quality > 1024) current_quality = 1024; @@ -321,12 +325,13 @@ static ssize_t hwrng_attr_current_store(struct device *dev, const char *buf, size_t len) { int err = -ENODEV; - struct hwrng *rng; + struct hwrng *rng, *old_rng, *new_rng; err = mutex_lock_interruptible(&rng_mutex); if (err) return -ERESTARTSYS; + old_rng = current_rng; if (sysfs_streq(buf, "")) { err = enable_best_rng(); } else { @@ -338,9 +343,15 @@ static ssize_t hwrng_attr_current_store(struct device *dev, } } } - + new_rng = get_current_rng_nolock(); mutex_unlock(&rng_mutex); + if (new_rng) { + if (new_rng != old_rng) + add_early_randomness(new_rng); + put_rng(new_rng); + } + return err ? : len; } @@ -460,13 +471,15 @@ static void start_khwrngd(void) int hwrng_register(struct hwrng *rng) { int err = -EINVAL; - struct hwrng *old_rng, *tmp; + struct hwrng *tmp; struct list_head *rng_list_ptr; + bool is_new_current = false; if (!rng->name || (!rng->data_read && !rng->read)) goto out; mutex_lock(&rng_mutex); + /* Must not register two RNGs with the same name. */ err = -EEXIST; list_for_each_entry(tmp, &rng_list, list) { @@ -485,10 +498,8 @@ int hwrng_register(struct hwrng *rng) } list_add_tail(&rng->list, rng_list_ptr); - old_rng = current_rng; - err = 0; - if (!old_rng || - (!cur_rng_set_by_user && rng->quality > old_rng->quality)) { + if (!current_rng || + (!cur_rng_set_by_user && rng->quality > current_rng->quality)) { /* * Set new rng as current as the new rng source * provides better entropy quality and was not @@ -497,19 +508,26 @@ int hwrng_register(struct hwrng *rng) err = set_current_rng(rng); if (err) goto out_unlock; + /* to use current_rng in add_early_randomness() we need + * to take a ref + */ + is_new_current = true; + kref_get(&rng->ref); } - - if (old_rng && !rng->init) { + mutex_unlock(&rng_mutex); + if (is_new_current || !rng->init) { /* * Use a new device's input to add some randomness to * the system. If this rng device isn't going to be * used right away, its init function hasn't been - * called yet; so only use the randomness from devices - * that don't need an init callback. + * called yet by set_current_rng(); so only use the + * randomness from devices that don't need an init callback */ add_early_randomness(rng); } - + if (is_new_current) + put_rng(rng); + return 0; out_unlock: mutex_unlock(&rng_mutex); out: @@ -519,10 +537,12 @@ EXPORT_SYMBOL_GPL(hwrng_register); void hwrng_unregister(struct hwrng *rng) { + struct hwrng *old_rng, *new_rng; int err; mutex_lock(&rng_mutex); + old_rng = current_rng; list_del(&rng->list); if (current_rng == rng) { err = enable_best_rng(); @@ -532,6 +552,7 @@ void hwrng_unregister(struct hwrng *rng) } } + new_rng = get_current_rng_nolock(); if (list_empty(&rng_list)) { mutex_unlock(&rng_mutex); if (hwrng_fill) @@ -539,6 +560,12 @@ void hwrng_unregister(struct hwrng *rng) } else mutex_unlock(&rng_mutex); + if (new_rng) { + if (old_rng != new_rng) + add_early_randomness(new_rng); + put_rng(new_rng); + } + wait_for_completion(&rng->cleanup_done); } EXPORT_SYMBOL_GPL(hwrng_unregister);