[PATCH 1/2 v2] x86, irq: get correct available vectors for cpu disable

From: Prarit Bhargava
Date: Thu May 15 2014 - 09:25:33 EST


From: Yinghai Lu <yinghai@xxxxxxxxxx>

check_irq_vectors_for_cpu_disable() may overestimate the number of
available vectors assigned to a cpu. This can cause cpu remove to
erroneously fail.

commit da6139e49c7cb0f4251265cb5243b8d220adb48d, x86: Add check for
number of available vectors before CPU down, introduces a check to see if
there are enough empty vectors in the system to replace a downed cpu's
vectors. Code inspection shows that the range used in the check
(currently from FIRST_EXTERNAL_VECTOR to NR_VECTORS) is incorrect and
should be FIRST_EXTERNAL_VECTOR to first_system_vector. The value of
first_system_vector is decremented when system vectors are assigned in
alloc_system_vector().

The check_irq_vectors_for_cpu_disable() check also does not take into
account the first 32 system vectors which are not managed in the per_cpu
vector_irq arrays, including IA32_SYSCALL_VECTOR (0x80) and the
IRQ_MOVE_CLEANUP_VECTOR (0x20).

Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Prarit Bhargava <prarit@xxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
Cc: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx>
Cc: Yinghai Lu <yinghai@xxxxxxxxxx>
Cc: "Elliott, Robert (Server Storage)" <Elliott@xxxxxx>
Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx>

[v2]: fixed up typos
---
arch/x86/kernel/irq.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 283a76a..276b02b 100644
--- a/arch/x86/kernel/irq.c
+++ b/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>
@@ -334,8 +335,21 @@ int check_irq_vectors_for_cpu_disable(void)
for_each_online_cpu(cpu) {
if (cpu == this_cpu)
continue;
- for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS;
- vector++) {
+
+ /*
+ * assign_irq_vector() only scans per_cpu vectors from
+ * FIRST_EXTERNAL_VECTOR to first_system_vector.
+ * It also skips 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++;
}
--
1.7.9.3

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