[PATCH] x86_64: Fix race in TSC synchronization
Plug a race in TSC synchronization
We need to do tsc_sync_wait() before the CPU is set online to prevent
multiple CPUs from doing it in parallel - which won't work because TSC
sync has global unprotected state.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/arch/x86_64/kernel/smpboot.c b/arch/x86_64/kernel/smpboot.c
index b15761f..fa25e39 100644
--- a/arch/x86_64/kernel/smpboot.c
+++ b/arch/x86_64/kernel/smpboot.c
@@ -492,6 +492,14 @@
*/
set_cpu_sibling_map(smp_processor_id());
+ /*
+ * Wait for TSC sync to not schedule things before.
+ * We still process interrupts, which could see an inconsistent
+ * time in that window unfortunately.
+ * Do this here because TSC sync has global unprotected state.
+ */
+ tsc_sync_wait();
+
/*
* We need to hold call_lock, so there is no inconsistency
* between the time smp_call_function() determines number of
@@ -509,13 +517,6 @@
per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE;
unlock_ipi_call_lock();
- mb();
-
- /* Wait for TSC sync to not schedule things before.
- We still process interrupts, which could see an inconsistent
- time in that window unfortunately. */
- tsc_sync_wait();
-
cpu_idle();
}