From patchwork Tue Nov 27 15:05:20 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [055/270] ARM: OMAP: counter: add locking to read_persistent_clock Date: Tue, 27 Nov 2012 05:05:20 -0000 From: Ben Hutchings X-Patchwork-Id: 202239 Message-Id: <1354028720.4266.55.camel@deadeye.wl.decadent.org.uk> To: Greg Kroah-Hartman Cc: Tony Lindgren , linux-kernel@vger.kernel.org, stable@vger.kernel.org, R Sricharan , kernel-team@lists.ubuntu.com, Colin Cross On Mon, 2012-11-26 at 14:55 -0200, Herton Ronaldo Krzesinski wrote: > 3.5.7u1 -stable review patch. If anyone has any objections, please let me know. > > ------------------ > > From: Colin Cross > > commit 9d7d6e363b06934221b81a859d509844c97380df upstream. > > read_persistent_clock uses a global variable, use a spinlock to > ensure non-atomic updates to the variable don't overlap and cause > time to move backwards. > > Signed-off-by: Colin Cross > Signed-off-by: R Sricharan > Signed-off-by: Tony Lindgren > Signed-off-by: Herton Ronaldo Krzesinski [...] This is also missing from 3.4. I'm attaching the adjusted version for 3.2, which looks like it will work for 3.4. Ben. From: Colin Cross Date: Mon, 8 Oct 2012 14:01:12 -0700 Subject: ARM: OMAP: counter: add locking to read_persistent_clock commit 9d7d6e363b06934221b81a859d509844c97380df upstream. read_persistent_clock uses a global variable, use a spinlock to ensure non-atomic updates to the variable don't overlap and cause time to move backwards. Signed-off-by: Colin Cross Signed-off-by: R Sricharan Signed-off-by: Tony Lindgren [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings --- arch/arm/plat-omap/counter_32k.c | 21 ++++++++++++++------- 1 file changed, 14 insertions(+), 7 deletions(-) --- a/arch/arm/plat-omap/counter_32k.c +++ b/arch/arm/plat-omap/counter_32k.c @@ -82,22 +82,29 @@ static void notrace omap_update_sched_cl * nsecs and adds to a monotonically increasing timespec. */ static struct timespec persistent_ts; -static cycles_t cycles, last_cycles; +static cycles_t cycles; static unsigned int persistent_mult, persistent_shift; +static DEFINE_SPINLOCK(read_persistent_clock_lock); + void read_persistent_clock(struct timespec *ts) { unsigned long long nsecs; - cycles_t delta; - struct timespec *tsp = &persistent_ts; + cycles_t last_cycles; + unsigned long flags; + + spin_lock_irqsave(&read_persistent_clock_lock, flags); last_cycles = cycles; cycles = timer_32k_base ? __raw_readl(timer_32k_base) : 0; - delta = cycles - last_cycles; - nsecs = clocksource_cyc2ns(delta, persistent_mult, persistent_shift); + nsecs = clocksource_cyc2ns(cycles - last_cycles, + persistent_mult, persistent_shift); + + timespec_add_ns(&persistent_ts, nsecs); + + *ts = persistent_ts; - timespec_add_ns(tsp, nsecs); - *ts = *tsp; + spin_unlock_irqrestore(&read_persistent_clock_lock, flags); } int __init omap_init_clocksource_32k(void)