Patch "x86/smpboot: Make optimization of delay calibration work correctly" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

x86/smpboot: Make optimization of delay calibration work correctly

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-smpboot-make-optimization-of-delay-calibration-work-correctly.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Pavel Tatashin <[email protected]>
Date: Fri, 27 Oct 2017 20:11:00 -0400
Subject: x86/smpboot: Make optimization of delay calibration work correctly

From: Pavel Tatashin <[email protected]>

commit 76ce7cfe35ef58f34e6ba85327afb5fbf6c3ff9b upstream.

If the TSC has constant frequency then the delay calibration can be skipped when it has been calibrated for a package already. This is checked in calibrate_delay_is_known(), but that function is buggy in two aspects:

It returns 'false' if

  (!tsc_disabled && !cpu_has(&cpu_data(cpu), X86_FEATURE_CONSTANT_TSC)

which is obviously the reverse of the intended check and the check for the sibling mask cannot work either because the topology links have not been set up yet.

Correct the condition and move the call to set_cpu_sibling_map() before invoking calibrate_delay() so the sibling check works correctly.

[ tglx: Rewrote changelong ]

---
 arch/x86/kernel/smpboot.c |   11 ++++++-----
 arch/x86/kernel/tsc.c     |    8 +++-----
 2 files changed, 9 insertions(+), 10 deletions(-)

@@ -181,6 +181,12 @@ static void smp_callin(void)
 	smp_store_cpu_info(cpuid);
 
 	/*
+	 * The topology information must be up to date before
+	 * calibrate_delay() and notify_cpu_starting().
+	 */
+	set_cpu_sibling_map(raw_smp_processor_id());
+
+	/*
 	 * Get our bogomips.
 	 * Update loops_per_jiffy in cpu_data. Previous call to
 	 * smp_store_cpu_info() stored a value that is close but not as

@@ -190,11 +196,6 @@ static void smp_callin(void)
 	cpu_data(cpuid).loops_per_jiffy = loops_per_jiffy;
 	pr_debug("Stack at about %p\n", &cpuid);
 
-	/*
-	 * This must be done before setting cpu_online_mask
-	 * or calling notify_cpu_starting.
-	 */
-	set_cpu_sibling_map(raw_smp_processor_id());
 	wmb();
 
 	notify_cpu_starting(cpuid);

@@ -1382,12 +1382,10 @@ void __init tsc_init(void)
 unsigned long calibrate_delay_is_known(void)
 {
 	int sibling, cpu = smp_processor_id();
-	struct cpumask *mask = topology_core_cpumask(cpu);
+	int constant_tsc = cpu_has(&cpu_data(cpu), X86_FEATURE_CONSTANT_TSC);
+	const struct cpumask *mask = topology_core_cpumask(cpu);
 
-	if (!tsc_disabled && !cpu_has(&cpu_data(cpu), X86_FEATURE_CONSTANT_TSC))
-		return 0;
-
-	if (!mask)
+	if (tsc_disabled || !constant_tsc || !mask)
 		return 0;
 
 	sibling = cpumask_any_but(mask, cpu);

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/x86-smpboot-make-optimization-of-delay-calibration-work-correctly.patch