[Xen-changelog] Fix save/restore -- too much work being done in

[Xen patchbot -unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID a37a4abc11917196061b9da8bb026eac9153ef25
# Parent  89b1b67fc2c4111d6eece1adab8dbcfae6dd069f
Fix save/restore -- too much work being done in
interrupts-off context.
Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>

diff -r 89b1b67fc2c4 -r a37a4abc1191 
linux-2.6-xen-sparse/arch/xen/kernel/reboot.c
--- a/linux-2.6-xen-sparse/arch/xen/kernel/reboot.c     Wed Oct  5 15:54:09 2005
+++ b/linux-2.6-xen-sparse/arch/xen/kernel/reboot.c     Wed Oct  5 16:07:01 2005
@@ -95,25 +95,20 @@
 
        xenbus_suspend();
 
-       preempt_disable();
+       lock_cpu_hotplug();
 #ifdef CONFIG_SMP
-       /* Take all of the other cpus offline.  We need to be careful not
-          to get preempted between the final test for num_online_cpus()
-          == 1 and disabling interrupts, since otherwise userspace could
-          bring another cpu online, and then we'd be stuffed.  At the
-          same time, cpu_down can reschedule, so we need to enable
-          preemption while doing that.  This kind of sucks, but should be
-          correct. */
-       /* (We don't need to worry about other cpus bringing stuff up,
-          since by the time num_online_cpus() == 1, there aren't any
-          other cpus) */
+       /*
+        * Take all other CPUs offline. We hold the hotplug semaphore to
+        * avoid other processes bringing up CPUs under our feet.
+        */
        cpus_clear(prev_online_cpus);
        while (num_online_cpus() > 1) {
-               preempt_enable();
                for_each_online_cpu(i) {
                        if (i == 0)
                                continue;
+                       unlock_cpu_hotplug();
                        err = cpu_down(i);
+                       lock_cpu_hotplug();
                        if (err != 0) {
                                printk(KERN_CRIT "Failed to take all CPUs "
                                       "down: %d.\n", err);
@@ -121,29 +116,32 @@
                        }
                        cpu_set(i, prev_online_cpus);
                }
-               preempt_disable();
-       }
-#endif
-
-       __cli();
-
-       preempt_enable();
-
-       gnttab_suspend();
+       }
+#endif
+
+       preempt_disable();
 
 #ifdef __i386__
        mm_pin_all();
        kmem_cache_shrink(pgd_cache);
 #endif
 
+       __cli();
+       preempt_enable();
+       unlock_cpu_hotplug();
+
+       gnttab_suspend();
+
        HYPERVISOR_shared_info = (shared_info_t *)empty_zero_page;
        clear_fixmap(FIX_SHARED_INFO);
 
        xen_start_info->store_mfn = mfn_to_pfn(xen_start_info->store_mfn);
        xen_start_info->console_mfn = mfn_to_pfn(xen_start_info->console_mfn);
 
-       /* We'll stop somewhere inside this hypercall.  When it returns,
-          we'll start resuming after the restore. */
+       /*
+        * We'll stop somewhere inside this hypercall. When it returns,
+        * we'll start resuming after the restore.
+        */
        HYPERVISOR_suspend(virt_to_mfn(xen_start_info));
 
        shutting_down = SHUTDOWN_INVALID; 

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