[PATCH v6 3/3] PM: hibernate: fix spurious GFP mask WARNING in uswsusp path

[Youngjun Park <youngjun.park@lge.com>]

Commit 35e4a69b2003f ("PM: sleep: Allow pm_restrict_gfp_mask()
stacking") introduced refcount-based GFP mask management that warns
when pm_restore_gfp_mask() is called with saved_gfp_count == 0:

  WARNING: kernel/power/main.c:44 at pm_restore_gfp_mask+0xd7/0xf0
  CPU: 0 UID: 0 PID: 373 Comm: s2disk
  Call Trace:
   snapshot_ioctl+0x964/0xbd0
   __x64_sys_ioctl+0x724/0x1320
  ...

The uswsusp path calls pm_restore_gfp_mask() defensively in
SNAPSHOT_CREATE_IMAGE, SNAPSHOT_UNFREEZE, and snapshot_release(),
where the GFP mask may or may not be restricted depending on the
execution path.

Before the stacking change this was a silent no-op; it now triggers
a WARNING when saved_gfp_count is 0.

Introduce pm_restore_gfp_mask_safe(), which skips the call if
saved_gfp_count is 0. This avoids the warning without requiring
state tracking in snapshot_ioctl, which could otherwise leave the
GFP mask permanently restricted if mismanaged.

Fixes: 35e4a69b2003f ("PM: sleep: Allow pm_restrict_gfp_mask() stacking")
Signed-off-by: Youngjun Park <youngjun.park@lge.com>
---
 include/linux/suspend.h |  1 +
 kernel/power/main.c     | 18 ++++++++++++++++++
 kernel/power/user.c     |  6 +++---
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/include/linux/suspend.h b/include/linux/suspend.h
index b02876f1ae38..7777931d88a5 100644
--- a/include/linux/suspend.h
+++ b/include/linux/suspend.h
@@ -454,6 +454,7 @@ extern void pm_report_hw_sleep_time(u64 t);
 extern void pm_report_max_hw_sleep(u64 t);
 void pm_restrict_gfp_mask(void);
 void pm_restore_gfp_mask(void);
+void pm_restore_gfp_mask_safe(void);
 
 #define pm_notifier(fn, pri) {				\
 	static struct notifier_block fn##_nb =			\
diff --git a/kernel/power/main.c b/kernel/power/main.c
index 5f8c9e12eaec..90e9bd56a433 100644
--- a/kernel/power/main.c
+++ b/kernel/power/main.c
@@ -36,6 +36,24 @@
 static unsigned int saved_gfp_count;
 static gfp_t saved_gfp_mask;
 
+/**
+ * pm_restore_gfp_mask_safe - Conditionally restore the GFP mask
+ *
+ * Call pm_restore_gfp_mask() only if a GFP restriction is active.
+ *
+ * After GFP mask stacking was introduced, calling
+ * pm_restore_gfp_mask() without a matching restriction triggers a
+ * warning. Some hibernation paths invoke restore defensively, so this
+ * helper avoids spurious warnings when no restriction is in place.
+ */
+void pm_restore_gfp_mask_safe(void)
+{
+	WARN_ON(!mutex_is_locked(&system_transition_mutex));
+	if (!saved_gfp_count)
+		return;
+	pm_restore_gfp_mask();
+}
+
 void pm_restore_gfp_mask(void)
 {
 	WARN_ON(!mutex_is_locked(&system_transition_mutex));
diff --git a/kernel/power/user.c b/kernel/power/user.c
index aab9aece1009..88de4b76a9dc 100644
--- a/kernel/power/user.c
+++ b/kernel/power/user.c
@@ -119,7 +119,7 @@ static int snapshot_release(struct inode *inode, struct file *filp)
 	free_all_swap_pages(data->swap);
 	unpin_hibernation_swap_type(data->swap);
 	if (data->frozen) {
-		pm_restore_gfp_mask();
+		pm_restore_gfp_mask_safe();
 		free_basic_memory_bitmaps();
 		thaw_processes();
 	} else if (data->free_bitmaps) {
@@ -306,7 +306,7 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 	case SNAPSHOT_UNFREEZE:
 		if (!data->frozen || data->ready)
 			break;
-		pm_restore_gfp_mask();
+		pm_restore_gfp_mask_safe();
 		free_basic_memory_bitmaps();
 		data->free_bitmaps = false;
 		thaw_processes();
@@ -318,7 +318,7 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 			error = -EPERM;
 			break;
 		}
-		pm_restore_gfp_mask();
+		pm_restore_gfp_mask_safe();
 		error = hibernation_snapshot(data->platform_support);
 		if (!error) {
 			error = put_user(in_suspend, (int __user *)arg);
-- 
2.34.1