From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757412AbaIRCwE (ORCPT ); Wed, 17 Sep 2014 22:52:04 -0400 Received: from ozlabs.org ([103.22.144.67]:51642 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756996AbaIRCwB (ORCPT ); Wed, 17 Sep 2014 22:52:01 -0400 From: Rusty Russell To: Amos Kong , virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, herbert@gondor.apana.org.au, m@bues.ch, mb@bu3sch.de, mpm@selenic.com, amit.shah@redhat.com, linux-kernel@vger.kernel.org Cc: Rusty Russell Subject: [PATCH 3/5] hw_random: fix unregister race. Date: Thu, 18 Sep 2014 12:18:24 +0930 Message-Id: <1411008506-28349-3-git-send-email-rusty@rustcorp.com.au> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1411008506-28349-1-git-send-email-rusty@rustcorp.com.au> References: <87wq91odhf.fsf@rustcorp.com.au> <1411008506-28349-1-git-send-email-rusty@rustcorp.com.au> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The previous patch added one potential problem: we can still be reading from a hwrng when it's unregistered. Add a wait for zero in the hwrng_unregister path. Signed-off-by: Rusty Russell --- drivers/char/hw_random/core.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index dc9092a1075d..b4a21e9521cf 100644 --- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -60,6 +60,7 @@ static DEFINE_MUTEX(rng_mutex); static DEFINE_MUTEX(reading_mutex); static int data_avail; static u8 *rng_buffer, *rng_fillbuf; +static DECLARE_WAIT_QUEUE_HEAD(rng_done); static unsigned short current_quality; static unsigned short default_quality; /* = 0; default to "off" */ @@ -98,6 +99,7 @@ static inline void cleanup_rng(struct kref *kref) if (rng->cleanup) rng->cleanup(rng); + wake_up_all(&rng_done); } static void set_current_rng(struct hwrng *rng) @@ -529,6 +531,9 @@ void hwrng_unregister(struct hwrng *rng) } mutex_unlock(&rng_mutex); + + /* Just in case rng is reading right now, wait. */ + wait_event(rng_done, atomic_read(&rng->ref.refcount) == 0); } EXPORT_SYMBOL_GPL(hwrng_unregister); -- 1.9.1