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, 12 insertions, 6 deletions

diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index 3b354560f306..aa6320207745 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -579,11 +579,13 @@ static bool is_async(struct device *dev)
  * Execute the appropriate "resume" callback for all devices whose status
  * indicates that they are suspended.
  */
-static void dpm_resume(pm_message_t state)
+void dpm_resume(pm_message_t state)
 {
         struct device *dev;
         ktime_t starttime = ktime_get();
 
+        might_sleep();
+
         mutex_lock(&dpm_list_mtx);
         pm_transition = state;
         async_error = 0;
@@ -656,10 +658,12 @@ static void device_complete(struct device *dev, pm_message_t state)
  * Execute the ->complete() callbacks for all devices whose PM status is not
  * DPM_ON (this allows new devices to be registered).
  */
-static void dpm_complete(pm_message_t state)
+void dpm_complete(pm_message_t state)
 {
         struct list_head list;
 
+        might_sleep();
+
         INIT_LIST_HEAD(&list);
         mutex_lock(&dpm_list_mtx);
         while (!list_empty(&dpm_prepared_list)) {
@@ -688,7 +692,6 @@ static void dpm_complete(pm_message_t state)
  */
 void dpm_resume_end(pm_message_t state)
 {
-        might_sleep();
         dpm_resume(state);
         dpm_complete(state);
 }
@@ -912,11 +915,13 @@ static int device_suspend(struct device *dev)
  * dpm_suspend - Execute "suspend" callbacks for all non-sysdev devices.
  * @state: PM transition of the system being carried out.
  */
-static int dpm_suspend(pm_message_t state)
+int dpm_suspend(pm_message_t state)
 {
         ktime_t starttime = ktime_get();
         int error = 0;
 
+        might_sleep();
+
         mutex_lock(&dpm_list_mtx);
         pm_transition = state;
         async_error = 0;
@@ -1003,10 +1008,12 @@ static int device_prepare(struct device *dev, pm_message_t state)
  *
  * Execute the ->prepare() callback(s) for all devices.
  */
-static int dpm_prepare(pm_message_t state)
+int dpm_prepare(pm_message_t state)
 {
         int error = 0;
 
+        might_sleep();
+
         mutex_lock(&dpm_list_mtx);
         while (!list_empty(&dpm_list)) {
                 struct device *dev = to_device(dpm_list.next);
@@ -1055,7 +1062,6 @@ int dpm_suspend_start(pm_message_t state)
 {
         int error;
 
-        might_sleep();
         error = dpm_prepare(state);
         if (!error)
                 error = dpm_suspend(state);