# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1273833555 -3600
# Node ID 578375084a9ee1063f4bc5a8e64e59677804cdb9
# Parent 9ff084bae83a1506f731ff6a926fefcccec5b1b1
x86: Do no thold cpu_add_remove_lock across stop_machine_run().
Instead we protect against concurrent online/offline requests for a
single CPU asynchronously, using a cpumask for bookkeeping.
This means that cpu_add_remove_lock no longer needs to be acquired via
spin_trylock.
Signed-off-by: Keir Fraser <keir.fraser@xxxxxxxxxx>
---
xen/arch/x86/platform_hypercall.c | 7 -----
xen/arch/x86/smpboot.c | 49 ++++++++++++++++++--------------------
2 files changed, 25 insertions(+), 31 deletions(-)
diff -r 9ff084bae83a -r 578375084a9e xen/arch/x86/platform_hypercall.c
--- a/xen/arch/x86/platform_hypercall.c Fri May 14 10:13:30 2010 +0100
+++ b/xen/arch/x86/platform_hypercall.c Fri May 14 11:39:15 2010 +0100
@@ -409,12 +409,7 @@ ret_t do_platform_op(XEN_GUEST_HANDLE(xe
g_info = &op->u.pcpu_info;
- /* spin_trylock() avoids deadlock with stop_machine_run(). */
- if ( !spin_trylock(&cpu_add_remove_lock) )
- {
- ret = -EBUSY;
- break;
- }
+ spin_lock(&cpu_add_remove_lock);
if ( (g_info->xen_cpuid >= NR_CPUS) ||
(g_info->xen_cpuid < 0) ||
diff -r 9ff084bae83a -r 578375084a9e xen/arch/x86/smpboot.c
--- a/xen/arch/x86/smpboot.c Fri May 14 10:13:30 2010 +0100
+++ b/xen/arch/x86/smpboot.c Fri May 14 11:39:15 2010 +0100
@@ -1330,24 +1330,25 @@ static int take_cpu_down(void *unused)
return __cpu_disable();
}
+/*
+ * Protects against concurrent offline/online requests for a single CPU.
+ * We need this extra protection because cpu_down() cannot continuously hold
+ * the cpu_add_remove_lock, as it cannot be held across stop_machine_run().
+ */
+static cpumask_t cpu_offlining;
+
int cpu_down(unsigned int cpu)
{
int err = 0;
- /* spin_trylock() avoids deadlock with stop_machine_run(). */
- if (!spin_trylock(&cpu_add_remove_lock))
- return -EBUSY;
-
- /* Can not offline BSP */
- if (cpu == 0) {
- err = -EINVAL;
- goto out;
- }
-
- if (!cpu_online(cpu)) {
- err = -EINVAL;
- goto out;
- }
+ spin_lock(&cpu_add_remove_lock);
+
+ if ((cpu == 0) || !cpu_online(cpu) || cpu_isset(cpu, cpu_offlining)) {
+ spin_unlock(&cpu_add_remove_lock);
+ return -EINVAL;
+ }
+
+ cpu_set(cpu, cpu_offlining);
err = cpupool_cpu_remove(cpu);
if (err)
@@ -1357,14 +1358,16 @@ int cpu_down(unsigned int cpu)
cpufreq_del_cpu(cpu);
+ spin_unlock(&cpu_add_remove_lock);
err = stop_machine_run(take_cpu_down, NULL, cpu);
+ spin_lock(&cpu_add_remove_lock);
+
if (err < 0) {
cpupool_cpu_add(cpu);
goto out;
}
__cpu_die(cpu);
-
BUG_ON(cpu_online(cpu));
migrate_tasklets_from_cpu(cpu);
@@ -1373,6 +1376,7 @@ out:
out:
if (!err)
send_guest_global_virq(dom0, VIRQ_PCPU_STATE);
+ cpu_clear(cpu, cpu_offlining);
spin_unlock(&cpu_add_remove_lock);
return err;
}
@@ -1381,13 +1385,10 @@ int cpu_up(unsigned int cpu)
{
int err = 0;
- /* spin_trylock() avoids deadlock with stop_machine_run(). */
- if (!spin_trylock(&cpu_add_remove_lock))
- return -EBUSY;
-
- if (cpu_online(cpu)) {
- printk("Bring up a online cpu. Bogus!\n");
- err = -EBUSY;
+ spin_lock(&cpu_add_remove_lock);
+
+ if (cpu_online(cpu) || cpu_isset(cpu, cpu_offlining)) {
+ err = -EINVAL;
goto out;
}
@@ -1485,9 +1486,7 @@ int cpu_add(uint32_t apic_id, uint32_t a
if ( physid_isset(apic_id, phys_cpu_present_map) )
return -EEXIST;
- /* spin_trylock() avoids deadlock with stop_machine_run(). */
- if (!spin_trylock(&cpu_add_remove_lock))
- return -EBUSY;
+ spin_lock(&cpu_add_remove_lock);
cpu = mp_register_lapic(apic_id, 1);
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