x86/smpboot: Remove APIC.wait_for_init_deassert and atomic init_deasserted

Both the per-APIC flag ".wait_for_init_deassert",
and the global atomic_t "init_deasserted"
are dead code -- remove them.

For all APIC types, "wait_for_master()"
prevents an AP from proceeding until the BSP has set
cpu_callout_mask, making "init_deasserted" {unnecessary}:

	BSP: <de-assert INIT>
	...
	BSP: {set init_deasserted}
	AP: wait_for_master()
		set cpu_initialized_mask
		wait for cpu_callout_mask
	BSP: test cpu_initialized_mask
	BSP: set cpu_callout_mask
	AP: test cpu_callout_mask
	AP: {wait for init_deasserted}
	...
	AP: <touch APIC>

Deleting the {dead code} above is necessary to enable
some parallelism in a future patch.

Signed-off-by: Len Brown <len.brown@intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Jan H. Schönherr <jschoenh@amazon.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Zhu Guihua <zhugh.fnst@cn.fujitsu.com>
Link: http://lkml.kernel.org/r/de4b3a9bab894735e285870b5296da25ee6a8a5a.1439739165.git.len.brown@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 3 insertions, 13 deletions

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 674026455fee..c15d0073c829 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -97,8 +97,6 @@ DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_llc_shared_map);
 DEFINE_PER_CPU_READ_MOSTLY(struct cpuinfo_x86, cpu_info);
 EXPORT_PER_CPU_SYMBOL(cpu_info);
 
-atomic_t init_deasserted;
-
 static inline void smpboot_setup_warm_reset_vector(unsigned long start_eip)
 {
 	unsigned long flags;
@@ -146,16 +144,11 @@ static void smp_callin(void)
 
 	/*
 	 * If waken up by an INIT in an 82489DX configuration
-	 * we may get here before an INIT-deassert IPI reaches
-	 * our local APIC.  We have to wait for the IPI or we'll
-	 * lock up on an APIC access.
-	 *
-	 * Since CPU0 is not wakened up by INIT, it doesn't wait for the IPI.
+	 * cpu_callout_mask guarantees we don't get here before
+	 * an INIT_deassert IPI reaches our local APIC, so it is
+	 * now safe to touch our local APIC.
 	 */
 	cpuid = smp_processor_id();
-	if (apic->wait_for_init_deassert && cpuid)
-		while (!atomic_read(&init_deasserted))
-			cpu_relax();
 
 	/*
 	 * (This works even if the APIC is not enabled.)
@@ -620,7 +613,6 @@ wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
 	send_status = safe_apic_wait_icr_idle();
 
 	mb();
-	atomic_set(&init_deasserted, 1);
 
 	/*
 	 * Should we send STARTUP IPIs ?
@@ -861,8 +853,6 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
 	 * the targeted processor.
 	 */
 
-	atomic_set(&init_deasserted, 0);
-
 	if (get_uv_system_type() != UV_NON_UNIQUE_APIC) {
 
 		pr_debug("Setting warm reset code and vector.\n");