[PATCH] Fix sync_tsc hang

sync_tsc was using smp_call_function to ask the boot processor to report
it's tsc value.  smp_call_function performs an IPI_send_allbutself which is
a broadcast ipi.  There is a window during processor startup during which
the target cpu has started and before it has initialized it's interrupt
vectors so it can properly process an interrupt.  Receveing an interrupt
during that window will triple fault the cpu and do other nasty things.

Why cli does not protect us from that is beyond me.

The simple fix is to match ia64 and provide a smp_call_function_single.
Which avoids the broadcast and is more efficient.

This certainly fixes the problem of getting stuck on boot which was
very easy to trigger on my SMP Hyperthreaded Xeon, and I think
it fixes it for the right reasons.

Minor changes by AK

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/asm-x86_64/smp.h b/include/asm-x86_64/smp.h
index 18ac762..de8b57b 100644
--- a/include/asm-x86_64/smp.h
+++ b/include/asm-x86_64/smp.h
@@ -49,6 +49,9 @@ extern int smp_num_siblings;
 extern void smp_send_reschedule(int cpu);
 extern void zap_low_mappings(void);
 void smp_stop_cpu(void);
+extern int smp_call_function_single(int cpuid, void (*func) (void *info),
+				void *info, int retry, int wait);
+
 extern cpumask_t cpu_sibling_map[NR_CPUS];
 extern cpumask_t cpu_core_map[NR_CPUS];
 extern u8 phys_proc_id[NR_CPUS];