From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757313Ab3CNKor (ORCPT ); Thu, 14 Mar 2013 06:44:47 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:52034 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756728Ab3CNKiD (ORCPT ); Thu, 14 Mar 2013 06:38:03 -0400 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: "Theodore Ts'o" , Luis Henriques Subject: [PATCH 67/88] random: fix locking dependency with the tasklist_lock Date: Thu, 14 Mar 2013 10:36:00 +0000 Message-Id: <1363257381-15900-68-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 1.8.1.2 In-Reply-To: <1363257381-15900-1-git-send-email-luis.henriques@canonical.com> References: <1363257381-15900-1-git-send-email-luis.henriques@canonical.com> X-Extended-Stable: 3.5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.5.7.8 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Theodore Ts'o commit b980955236922ae6106774511c5c05003d3ad225 upstream. Commit 6133705494bb introduced a circular lock dependency because posix_cpu_timers_exit() is called by release_task(), which is holding a writer lock on tasklist_lock, and this can cause a deadlock since kill_fasync() gets called with nonblocking_pool.lock taken. There's no reason why kill_fasync() needs to be taken while the random pool is locked, so move it out to fix this locking dependency. Signed-off-by: "Theodore Ts'o" Reported-by: Russ Dill Signed-off-by: Luis Henriques --- drivers/char/random.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index d98b2a6..91abbc4 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -855,6 +855,7 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min, int reserved) { unsigned long flags; + int wakeup_write = 0; /* Hold lock while accounting */ spin_lock_irqsave(&r->lock, flags); @@ -876,10 +877,8 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min, else r->entropy_count = reserved; - if (r->entropy_count < random_write_wakeup_thresh) { - wake_up_interruptible(&random_write_wait); - kill_fasync(&fasync, SIGIO, POLL_OUT); - } + if (r->entropy_count < random_write_wakeup_thresh) + wakeup_write = 1; } DEBUG_ENT("debiting %d entropy credits from %s%s\n", @@ -887,6 +886,11 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min, spin_unlock_irqrestore(&r->lock, flags); + if (wakeup_write) { + wake_up_interruptible(&random_write_wait); + kill_fasync(&fasync, SIGIO, POLL_OUT); + } + return nbytes; } -- 1.8.1.2