From patchwork Mon Nov 26 16:55:45 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: Mon, 26 Nov 2012 06:55:45 -0000 From: Herton Ronaldo Krzesinski X-Patchwork-Id: 201788 Message-Id: <1353949160-26803-56-git-send-email-herton.krzesinski@canonical.com> To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Tony Lindgren , R Sricharan , Colin Cross 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 --- arch/arm/plat-omap/counter_32k.c | 21 ++++++++++++++------- 1 file changed, 14 insertions(+), 7 deletions(-) diff --git a/arch/arm/plat-omap/counter_32k.c b/arch/arm/plat-omap/counter_32k.c index 2132c4f..721eae5 100644 --- a/arch/arm/plat-omap/counter_32k.c +++ b/arch/arm/plat-omap/counter_32k.c @@ -52,22 +52,29 @@ static u32 notrace omap_32k_read_sched_clock(void) * 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); + static void omap_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 = sync32k_cnt_reg ? __raw_readl(sync32k_cnt_reg) : 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); } /**