cpufreq: stats: Add memory barrier to store_reset() (efad4240) · Commits · 戴 / test

There is nothing to prevent the CPU or the compiler from reordering the writes to stats->reset_time and stats->reset_pending in store_reset(), in which case the readers of stats->reset_time may see a stale value. Moreover, on 32-bit arches the write to reset_time cannot be completed in one go, so the readers of it may see a partially updated value in that case. To prevent that from happening, add a write memory barrier between the writes to stats->reset_time and stats->reset_pending in store_reset() and corresponding read memory barrier in the readers of stats->reset_time. Fixes: ("cpufreq: stats: Defer stats update to cpufreq_stats_record_transition()") Signed-off-by:

Rafael J. Wysocki <rafael.j.wysocki@intel.com> Acked-by:

Viresh Kumar <viresh.kumar@linaro.org>

drivers/cpufreq/cpufreq_stats.c

+18 −2

Original line number	Diff line number	Diff line
		@@ -47,6 +47,11 @@ static void cpufreq_stats_reset_table(struct cpufreq_stats *stats)

		/* Adjust for the time elapsed since reset was requested */
		WRITE_ONCE(stats->reset_pending, 0);
		/*
		* Prevent the reset_time read from being reordered before the
		* reset_pending accesses in cpufreq_stats_record_transition().
		*/
		smp_rmb();
		cpufreq_stats_update(stats, READ_ONCE(stats->reset_time));
		}

		@@ -71,10 +76,16 @@ static ssize_t show_time_in_state(struct cpufreq_policy policy, char buf)

		for (i = 0; i < stats->state_num; i++) {
		if (pending) {
		if (i == stats->last_index)
		if (i == stats->last_index) {
		/*
		* Prevent the reset_time read from occurring
		* before the reset_pending read above.
		*/
		smp_rmb();
		time = get_jiffies_64() - READ_ONCE(stats->reset_time);
		else
		} else {
		time = 0;
		}
		} else {
		time = stats->time_in_state[i];
		if (i == stats->last_index)
		@@ -99,6 +110,11 @@ static ssize_t store_reset(struct cpufreq_policy policy, const char buf,
		* avoid races.
		*/
		WRITE_ONCE(stats->reset_time, get_jiffies_64());
		/*
		* The memory barrier below is to prevent the readers of reset_time from
		* seeing a stale or partially updated value.
		*/
		smp_wmb();
		WRITE_ONCE(stats->reset_pending, 1);

		return count;

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