[PATCH v3] x86, irq: get correct available vectors for cpu disable

[Yinghai Lu <yinghai@kernel.org>]

used_vectors is a bitmap for vectors that are not tracked in per_cpu
vector_irq.
used_vectors contains information on the first 32 exceptions, the system vectors.
the IA32_SYSCALL_VECTOR (0x80), and the IRQ_MOVE_CLEANUP_VECTOR (0x20).

assign_irq_vectors() assigns vectors up to first_system_vector and
it will not use vectors that are set used_vectors.

This patch modifies the code to scan up to first_system_vector
and do a test on the used_vectors bitmap.

So count avaiable vectors correctly.

-v2: fix compiling problem.
-v3: update changelog and commets

Signed-off-by: Yinghai Lu <yinghai@kernel.org>

---
 arch/x86/kernel/irq.c |   18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

Index: linux-2.6/arch/x86/kernel/irq.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/irq.c
+++ linux-2.6/arch/x86/kernel/irq.c
@@ -17,6 +17,7 @@
 #include <asm/idle.h>
 #include <asm/mce.h>
 #include <asm/hw_irq.h>
+#include <asm/desc.h>
 
 #define CREATE_TRACE_POINTS
 #include <asm/trace/irq_vectors.h>
@@ -321,8 +322,21 @@ int check_irq_vectors_for_cpu_disable(vo
 	for_each_online_cpu(cpu) {
 		if (cpu == this_cpu)
 			continue;
-		for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS;
-		     vector++) {
+
+		/*
+		 * assign_irq_vector() only scan per_cpu vectors from
+		 * FIRST_EXTERNAL_VECTOR to first_system_vector.
+		 * It aslo skip vectors that are set in used_vectors bitmask.
+		 * used_vectors could have bits set for
+		 *	IA32_SYSCALL_VECTOR (0x80)
+		 *	IRQ_MOVE_CLEANUP_VECTOR (0x20)
+		 * Don't count those as available vectors.
+		 */
+		for (vector = FIRST_EXTERNAL_VECTOR;
+		     vector < first_system_vector; vector++) {
+			if (test_bit(vector, used_vectors))
+				continue;
+
 			if (per_cpu(vector_irq, cpu)[vector] < 0)
 				count++;
 		}