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[Xen-devel] [PATCH][Linux] Fix access to xenstore hangs after hotremove CPU



Hi,

CPU hotplug doesn't support user-space event channels.

$ echo 0 > /sys/devices/system/cpu/cpu1/online
$ xenstore-ls
... hangs up ...

Attached patch fixes it.

Thanks,
Kouya

Signed-off-by: Kouya Shimura <kouya@xxxxxxxxxxxxxx>

diff -r fd879c0688bf drivers/xen/evtchn/evtchn.c
--- a/drivers/xen/evtchn/evtchn.c       Fri Nov 23 16:26:56 2007 +0000
+++ b/drivers/xen/evtchn/evtchn.c       Tue Nov 27 11:26:51 2007 +0900
@@ -231,6 +231,15 @@ static ssize_t evtchn_write(struct file 
        return rc;
 }
 
+static unsigned int next_bind_cpu(cpumask_t map)
+{
+       static unsigned int bind_cpu;
+       bind_cpu = next_cpu(bind_cpu, map);
+       if (bind_cpu >= NR_CPUS)
+               bind_cpu = first_cpu(map);
+       return bind_cpu;
+}
+
 static void evtchn_bind_to_user(struct per_user_data *u, int port)
 {
        spin_lock_irq(&port_user_lock);
@@ -238,13 +247,8 @@ static void evtchn_bind_to_user(struct p
        BUG_ON(port_user[port] != NULL);
        port_user[port] = u;
 
-       if (u->bind_cpu == -1) {
-               static unsigned int bind_cpu;
-               bind_cpu = next_cpu(bind_cpu, cpu_online_map);
-               if (bind_cpu >= NR_CPUS)
-                       bind_cpu = first_cpu(cpu_online_map);
-               u->bind_cpu = bind_cpu;
-       }
+       if (u->bind_cpu == -1)
+               u->bind_cpu = next_bind_cpu(cpu_online_map);
 
        rebind_evtchn_to_cpu(port, u->bind_cpu);
 
@@ -483,6 +487,42 @@ static struct miscdevice evtchn_miscdev 
        .fops         = &evtchn_fops,
 };
 
+#ifdef CONFIG_HOTPLUG_CPU
+#include <linux/cpu.h>
+
+static int evtchn_cpu_notify(struct notifier_block *nfb,
+                       unsigned long action, void *hcpu)
+{
+       int hotcpu = (unsigned long)hcpu;
+       cpumask_t map = cpu_online_map;
+       int port, newcpu;
+       struct per_user_data *u;
+
+       switch (action) {
+       case CPU_DOWN_PREPARE:
+               cpu_clear(hotcpu, map);
+               spin_lock_irq(&port_user_lock);
+               for (port = 0; port < NR_EVENT_CHANNELS; port++) {
+                       if ((u = port_user[port]) != NULL && 
+                           u->bind_cpu == hotcpu &&
+                           (newcpu = next_bind_cpu(map)) < NR_CPUS) {
+                               rebind_evtchn_to_cpu(port, newcpu);
+                               u->bind_cpu = newcpu;
+                       }
+               }
+               spin_unlock_irq(&port_user_lock);
+               break;
+       default:
+               return NOTIFY_DONE;
+       }
+       return NOTIFY_OK;
+}
+
+static struct notifier_block __cpuinitdata cpu_nfb = {
+       .notifier_call = evtchn_cpu_notify
+};
+#endif
+
 static int __init evtchn_init(void)
 {
        int err;
@@ -502,6 +542,9 @@ static int __init evtchn_init(void)
 
        printk("Event-channel device installed.\n");
 
+#ifdef CONFIG_HOTPLUG_CPU
+       register_cpu_notifier(&cpu_nfb);
+#endif
        return 0;
 }
 
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