Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753892AbcKILGr (ORCPT ); Wed, 9 Nov 2016 06:06:47 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:54278 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933368AbcKILGm (ORCPT ); Wed, 9 Nov 2016 06:06:42 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Ashton Holmes , Michael Thayer , Thomas Gleixner , Michal Necasek , Peter Zijlstra , knut.osmundsen@oracle.com, stern@rowland.harvard.edu, rt@linutronix.de Subject: [PATCH 4.8 043/138] timers: Prevent base clock corruption when forwarding Date: Wed, 9 Nov 2016 11:45:26 +0100 Message-Id: <20161109102846.645300547@linuxfoundation.org> X-Mailer: git-send-email 2.10.2 In-Reply-To: <20161109102844.808685475@linuxfoundation.org> References: <20161109102844.808685475@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3771 Lines: 115 4.8-stable review patch. If anyone has any objections, please let me know. ------------------ From: Thomas Gleixner commit 6bad6bccf2d717f652d37e63cf261eaa23466009 upstream. When a timer is enqueued we try to forward the timer base clock. This mechanism has two issues: 1) Forwarding a remote base unlocked The forwarding function is called from get_target_base() with the current timer base lock held. But if the new target base is a different base than the current base (can happen with NOHZ, sigh!) then the forwarding is done on an unlocked base. This can lead to corruption of base->clk. Solution is simple: Invoke the forwarding after the target base is locked. 2) Possible corruption due to jiffies advancing This is similar to the issue in get_net_timer_interrupt() which was fixed in the previous patch. jiffies can advance between check and assignement and therefore advancing base->clk beyond the next expiry value. So we need to read jiffies into a local variable once and do the checks and assignment with the local copy. Fixes: a683f390b93f("timers: Forward the wheel clock whenever possible") Reported-by: Ashton Holmes Reported-by: Michael Thayer Signed-off-by: Thomas Gleixner Cc: Michal Necasek Cc: Peter Zijlstra Cc: knut.osmundsen@oracle.com Cc: stern@rowland.harvard.edu Cc: rt@linutronix.de Link: http://lkml.kernel.org/r/20161022110552.253640125@linutronix.de Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman --- kernel/time/timer.c | 23 ++++++++++------------- 1 file changed, 10 insertions(+), 13 deletions(-) --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -878,7 +878,7 @@ static inline struct timer_base *get_tim #ifdef CONFIG_NO_HZ_COMMON static inline struct timer_base * -__get_target_base(struct timer_base *base, unsigned tflags) +get_target_base(struct timer_base *base, unsigned tflags) { #ifdef CONFIG_SMP if ((tflags & TIMER_PINNED) || !base->migration_enabled) @@ -891,25 +891,27 @@ __get_target_base(struct timer_base *bas static inline void forward_timer_base(struct timer_base *base) { + unsigned long jnow = READ_ONCE(jiffies); + /* * We only forward the base when it's idle and we have a delta between * base clock and jiffies. */ - if (!base->is_idle || (long) (jiffies - base->clk) < 2) + if (!base->is_idle || (long) (jnow - base->clk) < 2) return; /* * If the next expiry value is > jiffies, then we fast forward to * jiffies otherwise we forward to the next expiry value. */ - if (time_after(base->next_expiry, jiffies)) - base->clk = jiffies; + if (time_after(base->next_expiry, jnow)) + base->clk = jnow; else base->clk = base->next_expiry; } #else static inline struct timer_base * -__get_target_base(struct timer_base *base, unsigned tflags) +get_target_base(struct timer_base *base, unsigned tflags) { return get_timer_this_cpu_base(tflags); } @@ -917,14 +919,6 @@ __get_target_base(struct timer_base *bas static inline void forward_timer_base(struct timer_base *base) { } #endif -static inline struct timer_base * -get_target_base(struct timer_base *base, unsigned tflags) -{ - struct timer_base *target = __get_target_base(base, tflags); - - forward_timer_base(target); - return target; -} /* * We are using hashed locking: Holding per_cpu(timer_bases[x]).lock means @@ -1025,6 +1019,9 @@ __mod_timer(struct timer_list *timer, un } } + /* Try to forward a stale timer base clock */ + forward_timer_base(base); + timer->expires = expires; /* * If 'idx' was calculated above and the base time did not advance