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Commit 1eecd73c authored by Andi Kleen's avatar Andi Kleen Committed by Linus Torvalds
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[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: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 5e5ec104

arch/x86_64/kernel/smpboot.c

+8 −7
Original line number Diff line number Diff line
@@ -492,6 +492,14 @@ void __cpuinit start_secondary(void) 
	 */

	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 @@ void __cpuinit start_secondary(void) 
	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();

}