Re: [PATCH v5 3/3] PM: hibernate: fix spurious GFP mask WARNING in uswsusp path

["Rafael J. Wysocki" <rafael@kernel.org>]

On Thu, Mar 19, 2026 at 3:24 PM Youngjun Park <youngjun.park@lge.com> wrote:
>
> 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 and SNAPSHOT_UNFREEZE where the GFP mask may
> or may not be restricted depending on context (first call vs retry,
> hibernate vs resume). Before the stacking patch this was a silent
> no-op; now it triggers a WARNING.
>
> Introduce pm_restore_gfp_mask_safe() that skips the call when
> saved_gfp_count is 0. This is preferred over tracking the restrict
> state in snapshot_ioctl, as incorrect tracking risks leaving the
> GFP mask permanently restricted.
>
> 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     | 7 +++++++
>  kernel/power/user.c     | 4 ++--
>  3 files changed, 10 insertions(+), 2 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..e610a8c8b7ff 100644
> --- a/kernel/power/main.c
> +++ b/kernel/power/main.c
> @@ -36,6 +36,13 @@
>  static unsigned int saved_gfp_count;
>  static gfp_t saved_gfp_mask;
>
> +void pm_restore_gfp_mask_safe(void)
> +{
> +       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 3e41544b99d5..41cff6a89a1c 100644
> --- a/kernel/power/user.c
> +++ b/kernel/power/user.c
> @@ -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);
> --

AFAICS, this patch doesn't depend on the rest of the series, so I can
apply it separately unless there is a problem with that.

However, for the other 2 patches in the series, I'd need some tags
(preferably Reviewed-by) from mm people.

Thanks!