[PATCH] Revert "swsusp: disable nonboot CPUs before entering platform suspend"

This reverts commit 94985134b7b46848267ed6b734320db01c974e72 and
insteads removes the WARN_ON() that caused that commit in the first
place.

The problem is that we call disable_nonboot_cpus() in swsusp before
powering down the system in order to avoid triggering the WARN_ON()
in arch/x86_64/kernel/acpi/sleep.c:init_low_mapping() and this doesn't
work well on Thomas' system.

So instead, remove the WARN_ON() in arch/x86_64/kernel/acpi/sleep.c:
init_low_mapping(), which triggers every time during the suspend to disk
in the platform mode, as the potential problem it is related to doesn't
seem to occur in practice.

[ I think we might want to disallow the case of multiple users of that
  mm, or something.  Normally, playing with the current process page
  tables on the current CPU should be fine as long as we don't have
  other threads using those tables at the same time..

  Anyway, not pretty, but better than the warning or the lockup - Linus ]

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 4 insertions, 4 deletions

diff --git a/arch/x86_64/kernel/acpi/sleep.c b/arch/x86_64/kernel/acpi/sleep.c
index 23178ce6c783..e1548fbe95ae 100644
--- a/arch/x86_64/kernel/acpi/sleep.c
+++ b/arch/x86_64/kernel/acpi/sleep.c
@@ -66,8 +66,10 @@ static void init_low_mapping(void)
 {
         pgd_t *slot0 = pgd_offset(current->mm, 0UL);
         low_ptr = *slot0;
+        /* FIXME: We're playing with the current task's page tables here, which
+         * is potentially dangerous on SMP systems.
+         */
         set_pgd(slot0, *pgd_offset(current->mm, PAGE_OFFSET));
-        WARN_ON(num_online_cpus() != 1);
         local_flush_tlb();
 }
 
diff --git a/kernel/power/disk.c b/kernel/power/disk.c
index dee0ff40befd..aec19b063e3f 100644
--- a/kernel/power/disk.c
+++ b/kernel/power/disk.c
@@ -58,7 +58,6 @@ static inline int platform_prepare(void)
 
 static void power_down(suspend_disk_method_t mode)
 {
-        disable_nonboot_cpus();
         switch(mode) {
         case PM_DISK_PLATFORM:
                 if (pm_ops && pm_ops->enter) {
diff --git a/kernel/power/user.c b/kernel/power/user.c
index bf211fee1222..7cf6713b2325 100644
--- a/kernel/power/user.c
+++ b/kernel/power/user.c
@@ -401,10 +401,9 @@ static int snapshot_ioctl(struct inode *inode, struct file *filp,
 
                 case PMOPS_ENTER:
                         if (data->platform_suspend) {
-                                disable_nonboot_cpus();
                                 kernel_shutdown_prepare(SYSTEM_SUSPEND_DISK);
                                 error = pm_ops->enter(PM_SUSPEND_DISK);
-                                enable_nonboot_cpus();
+                                error = 0;
                         }
                         break;