| From | Greg Kroah-Hartman <> | Subject | [PATCH 3.15 092/109] x86, tsc: Fix cpufreq lockup | Date | Sat, 26 Jul 2014 12:02:54 -0700 |
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3.15-stable review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra <peterz@infradead.org>
commit 3896c329df8092661dac80f55a8c3f60136fd61a upstream.
Mauro reported that his AMD X2 using the powernow-k8 cpufreq driver locked up when doing cpu hotplug.
Because we called set_cyc2ns_scale() from the time_cpufreq_notifier() unconditionally, it gets called multiple times for each freq change, instead of only the once, when the tsc_khz value actually changes.
Because it gets called more than once, we run out of cyc2ns data slots and stall, waiting for a free one, but because we're half way offline, there's no consumers to free slots.
By placing the call inside the condition that actually changes tsc_khz we avoid superfluous calls and avoid the problem.
Reported-by: Mauro <registosites@hotmail.com> Tested-by: Mauro <registosites@hotmail.com> Fixes: 20d1c86a5776 ("sched/clock, x86: Rewrite cyc2ns() to avoid the need to disable IRQs") Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Bin Gao <bin.gao@intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mika Westerberg <mika.westerberg@linux.intel.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Stefani Seibold <stefani@seibold.net> Cc: linux-kernel@vger.kernel.org Signed-off-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- arch/x86/kernel/tsc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -920,9 +920,9 @@ static int time_cpufreq_notifier(struct tsc_khz = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new); if (!(freq->flags & CPUFREQ_CONST_LOOPS)) mark_tsc_unstable("cpufreq changes"); - } - set_cyc2ns_scale(tsc_khz, freq->cpu); + set_cyc2ns_scale(tsc_khz, freq->cpu); + } return 0; }
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