Jiang, Yunhong
2010-Mar-22 06:23 UTC
[Xen-devel] [PATCH] Not spin on the locks that be potentially held by stop_machine_run
Not spin on the locks that be potentially held by stop_machine_run
Currently stop_machine_run() will try to bring all CPUs to softirq context, with
some locks held, like xenpf_lock or cpu_add_remove_lock etc. However, if another
CPU is trying to get these locks, it may cause deadlock.
This patch replace all such spin_lock with spin_trylock. For xenpf_lock and
sysctl_lock, we try to use hypercall_continuation, so that we will not cause
trouble to user space tools. For cpu_hot_remove_lock, we simply return EBUSY if
failure, since it will only impact small number of user space tools.
In the end, we should try to make the stop_machine_run as spinlock free.
Signed-off-by: Jiang, Yunhong <yunhong.jiang@intel.com>
diff -r 2a31c8c8c7bd xen/arch/x86/platform_hypercall.c
--- a/xen/arch/x86/platform_hypercall.c Mon Mar 22 13:58:19 2010 +0800
+++ b/xen/arch/x86/platform_hypercall.c Mon Mar 22 13:58:21 2010 +0800
@@ -73,7 +73,10 @@ ret_t do_platform_op(XEN_GUEST_HANDLE(xe
if ( op->interface_version != XENPF_INTERFACE_VERSION )
return -EACCES;
- spin_lock(&xenpf_lock);
+ while ( !spin_trylock(&xenpf_lock) )
+ if ( hypercall_preempt_check() )
+ return hypercall_create_continuation(
+ __HYPERVISOR_platform_op, "h", u_xenpf_op);
switch ( op->cmd )
{
@@ -398,7 +401,11 @@ ret_t do_platform_op(XEN_GUEST_HANDLE(xe
g_info = &op->u.pcpu_info;
- spin_lock(&cpu_add_remove_lock);
+ if (!spin_trylock(&cpu_add_remove_lock))
+ {
+ ret = -EBUSY;
+ break;
+ }
if ( (g_info->xen_cpuid >= NR_CPUS) ||
(g_info->xen_cpuid < 0) ||
diff -r 2a31c8c8c7bd xen/arch/x86/smpboot.c
--- a/xen/arch/x86/smpboot.c Mon Mar 22 13:58:19 2010 +0800
+++ b/xen/arch/x86/smpboot.c Mon Mar 22 14:06:20 2010 +0800
@@ -1340,7 +1340,11 @@ int cpu_down(unsigned int cpu)
{
int err = 0;
- spin_lock(&cpu_add_remove_lock);
+ if ( !spin_trylock(&cpu_add_remove_lock) ) {
+ err = -EBUSY;
+ goto out;
+ }
+
if (num_online_cpus() == 1) {
err = -EBUSY;
goto out;
@@ -1382,7 +1386,9 @@ int cpu_up(unsigned int cpu)
{
int err = 0;
- spin_lock(&cpu_add_remove_lock);
+ if ( !spin_trylock(&cpu_add_remove_lock) )
+ return -EBUSY;
+
if (cpu_online(cpu)) {
printk("Bring up a online cpu. Bogus!\n");
err = -EBUSY;
@@ -1417,6 +1423,8 @@ void disable_nonboot_cpus(void)
if (cpu == 0)
continue;
error = cpu_down(cpu);
+ /* No need to check EBUSY here */
+ ASSERT(error != -EBUSY);
if (!error) {
cpu_set(cpu, frozen_cpus);
printk("CPU%d is down\n", cpu);
@@ -1437,6 +1445,8 @@ void enable_nonboot_cpus(void)
mtrr_aps_sync_begin();
for_each_cpu_mask(cpu, frozen_cpus) {
error = cpu_up(cpu);
+ /* No conflict will happen here */
+ ASSERT(error != -EBUSY);
if (!error) {
printk("CPU%d is up\n", cpu);
continue;
@@ -1479,7 +1489,8 @@ int cpu_add(uint32_t apic_id, uint32_t a
if ( physid_isset(apic_id, phys_cpu_present_map) )
return -EEXIST;
- spin_lock(&cpu_add_remove_lock);
+ if ( !spin_trylock(&cpu_add_remove_lock))
+ return -EBUSY;
cpu = mp_register_lapic(apic_id, 1);
diff -r 2a31c8c8c7bd xen/common/sysctl.c
--- a/xen/common/sysctl.c Mon Mar 22 13:58:19 2010 +0800
+++ b/xen/common/sysctl.c Mon Mar 22 13:58:21 2010 +0800
@@ -48,7 +48,10 @@ long do_sysctl(XEN_GUEST_HANDLE(xen_sysc
if ( op->interface_version != XEN_SYSCTL_INTERFACE_VERSION )
return -EACCES;
- spin_lock(&sysctl_lock);
+ while ( !spin_trylock(&sysctl_lock) )
+ if (hypercall_preempt_check() )
+ return hypercall_create_continuation(
+ __HYPERVISOR_sysctl, "h", u_sysctl);
switch ( op->cmd )
{
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