Re: [PATCH v2 6/6] super: add filesystem freezing helpers for suspend and hibernate

[Christian Brauner]

On Sat, Mar 29, 2025 at 09:42:19AM +0100, Christian Brauner wrote:
> Allow the power subsystem to support filesystem freeze for
> suspend and hibernate.
> 
> Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
> ---
>  fs/super.c         | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/fs.h |  2 ++
>  2 files changed, 57 insertions(+)
> 
> diff --git a/fs/super.c b/fs/super.c
> index 666a2a16df87..4364b763e91f 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -1176,6 +1176,61 @@ void emergency_thaw_all(void)
>  	}
>  }
>  
> +static inline bool get_active_super(struct super_block *sb)
> +{
> +	bool active;

Typo on my end. This is ofc bool active = false;
And fixed.

> +
> +	if (super_lock_excl(sb)) {
> +		active = atomic_inc_not_zero(&sb->s_active);
> +		super_unlock_excl(sb);
> +	}
> +	return active;
> +}
> +
> +static void filesystems_freeze_callback(struct super_block *sb, void *unused)
> +{
> +	if (!sb->s_op->freeze_fs && !sb->s_op->freeze_super)
> +		return;
> +
> +	if (!get_active_super(sb))
> +		return;
> +
> +	if (sb->s_op->freeze_super)
> +		sb->s_op->freeze_super(sb, FREEZE_MAY_NEST | FREEZE_HOLDER_KERNEL);
> +	else
> +		freeze_super(sb, FREEZE_MAY_NEST | FREEZE_HOLDER_KERNEL);
> +
> +	deactivate_super(sb);
> +}
> +
> +void filesystems_freeze(bool hibernate)
> +{
> +	__iterate_supers(filesystems_freeze_callback, NULL,
> +			 SUPER_ITER_UNLOCKED | SUPER_ITER_REVERSE);
> +}
> +
> +static void filesystems_thaw_callback(struct super_block *sb, void *unused)
> +{
> +	if (!sb->s_op->freeze_fs && !sb->s_op->freeze_super)
> +		return;
> +
> +	if (!get_active_super(sb))
> +		return;
> +
> +	if (sb->s_op->thaw_super)
> +		sb->s_op->thaw_super(sb, FREEZE_MAY_NEST | FREEZE_HOLDER_KERNEL);
> +	else
> +		thaw_super(sb, FREEZE_MAY_NEST | FREEZE_HOLDER_KERNEL);
> +
> +	deactivate_super(sb);
> +}
> +
> +void filesystems_thaw(bool hibernate)
> +{
> +	__iterate_supers(filesystems_thaw_callback, NULL,
> +			 SUPER_ITER_UNLOCKED | SUPER_ITER_REVERSE);
> +}
> +
>  static DEFINE_IDA(unnamed_dev_ida);
>  
>  /**
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index c475fa874055..29bd28491eff 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3518,6 +3518,8 @@ extern void drop_super_exclusive(struct super_block *sb);
>  extern void iterate_supers(void (*f)(struct super_block *, void *), void *arg);
>  extern void iterate_supers_type(struct file_system_type *,
>  			        void (*)(struct super_block *, void *), void *);
> +void filesystems_freeze(bool hibernate);
> +void filesystems_thaw(bool hibernate);
>  
>  extern int dcache_dir_open(struct inode *, struct file *);
>  extern int dcache_dir_close(struct inode *, struct file *);
> 
> -- 
> 2.47.2
>