x86: if we cannot calibrate the TSC, we panic.

The current tsc_init() clears the TSC feature bit if the TSC khz
cannot be calculated, causing us to panic in
arch/x86/kernel/cpu/bugs.c check_config().  We should simply mark it
unstable.

Frankly, someone should take an axe to this code.  mark_tsc_unstable()
not only marks it unstable, but sets tsc_enabled to 0, which seems
redundant but is actually important here because means it won't be
used by sched_clock() either.  Perhaps a tristate enum "UNUSABLE,
UNSTABLE, OK" would be clearer, and separate mark_tsc_unstable() and
mark_tsc_broken() functions?

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 5 insertions, 8 deletions

diff --git a/arch/x86/kernel/tsc_32.c b/arch/x86/kernel/tsc_32.c
index c2241e04ea5f..68657d8526fb 100644
--- a/arch/x86/kernel/tsc_32.c
+++ b/arch/x86/kernel/tsc_32.c
@@ -392,13 +392,15 @@ void __init tsc_init(void)
         int cpu;
 
         if (!cpu_has_tsc)
-                goto out_no_tsc;
+                return;
 
         cpu_khz = calculate_cpu_khz();
         tsc_khz = cpu_khz;
 
-        if (!cpu_khz)
-                goto out_no_tsc;
+        if (!cpu_khz) {
+                mark_tsc_unstable("could not calculate TSC khz");
+                return;
+        }
 
         printk("Detected %lu.%03lu MHz processor.\n",
                                 (unsigned long)cpu_khz / 1000,
@@ -431,9 +433,4 @@ void __init tsc_init(void)
                 tsc_enabled = 1;
 
         clocksource_register(&clocksource_tsc);
-
-        return;
-
-out_no_tsc:
-        setup_clear_cpu_cap(X86_FEATURE_TSC);
 }