PM: Allow drivers to allocate memory from .prepare() callbacks safely

If device drivers allocate substantial amounts of memory (above 1 MB)
in their hibernate .freeze() callbacks (or in their legacy suspend
callbcks during hibernation), the subsequent creation of hibernate
image may fail due to the lack of memory.  This is the case, because
the drivers' .freeze() callbacks are executed after the hibernate
memory preallocation has been carried out and the preallocated amount
of memory may be too small to cover the new driver allocations.
Unfortunately, the drivers' .prepare() callbacks also are executed
after the hibernate memory preallocation has completed, so they are
not suitable for allocating additional memory either.  Thus the only
way a driver can safely allocate memory during hibernation is to use
a hibernate/suspend notifier.  However, the notifiers are called
before the freezing of user space and the drivers wanting to use them
for allocating additional memory may not know how much memory needs
to be allocated at that point.

To let device drivers overcome this difficulty rework the hibernation
sequence so that the memory preallocation is carried out after the
drivers' .prepare() callbacks have been executed, so that the
.prepare() callbacks can be used for allocating additional memory
to be used by the drivers' .freeze() callbacks.  Update documentation
to match the new behavior of the code.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

1 files changed, 13 insertions, 4 deletions

diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index 95a2ac40f48c..f9bec56d8825 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -327,20 +327,25 @@ static int create_image(int platform_mode)
 
 int hibernation_snapshot(int platform_mode)
 {
+        pm_message_t msg = PMSG_RECOVER;
         int error;
 
         error = platform_begin(platform_mode);
         if (error)
                 goto Close;
 
+        error = dpm_prepare(PMSG_FREEZE);
+        if (error)
+                goto Complete_devices;
+
         /* Preallocate image memory before shutting down devices. */
         error = hibernate_preallocate_memory();
         if (error)
-                goto Close;
+                goto Complete_devices;
 
         suspend_console();
         pm_restrict_gfp_mask();
-        error = dpm_suspend_start(PMSG_FREEZE);
+        error = dpm_suspend(PMSG_FREEZE);
         if (error)
                 goto Recover_platform;
 
@@ -358,13 +363,17 @@ int hibernation_snapshot(int platform_mode)
         if (error || !in_suspend)
                 swsusp_free();
 
-        dpm_resume_end(in_suspend ?
-                (error ? PMSG_RECOVER : PMSG_THAW) : PMSG_RESTORE);
+        msg = in_suspend ? (error ? PMSG_RECOVER : PMSG_THAW) : PMSG_RESTORE;
+        dpm_resume(msg);
 
         if (error || !in_suspend)
                 pm_restore_gfp_mask();
 
         resume_console();
+
+ Complete_devices:
+        dpm_complete(msg);
+
  Close:
         platform_end(platform_mode);
         return error;