[patch 28/50] x86: disable TSC for sched_clock() when calibration failed

[Chris Wright]

-stable review patch.  If anyone has any objections, please let us know.
---------------------

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

upstream commit: 74dc51a3de06aa516e3b9fdc4017b2aeb38bf44b

When the TSC calibration fails then TSC is still used in
sched_clock(). Disable it completely in that case.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxx
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
---
 arch/x86/kernel/tsc_32.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/arch/x86/kernel/tsc_32.c
+++ b/arch/x86/kernel/tsc_32.c
@@ -401,6 +401,11 @@ void __init tsc_init(void)
 
 	if (!cpu_khz) {
 		mark_tsc_unstable("could not calculate TSC khz");
+		/*
+		 * We need to disable the TSC completely in this case
+		 * to prevent sched_clock() from using it.
+		 */
+		tsc_disabled = 1;
 		return;
 	}
 

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