linux-kernel - Re: [PATCH v2 4/6] super: use a common iterator (Part 1)

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Message-ID: <slv42oamhqmazebk42ka66gwbdenxm33as5vmz5djmt5weejrh@exf5sck3j2lb>
Date: Mon, 31 Mar 2025 12:01:57 +0200
From: Jan Kara <jack@...e.cz>
To: Christian Brauner <brauner@...nel.org>
Cc: linux-fsdevel@...r.kernel.org, jack@...e.cz, 
	linux-kernel@...r.kernel.org, James Bottomley <James.Bottomley@...senpartnership.com>, 
	mcgrof@...nel.org, hch@...radead.org, david@...morbit.com, rafael@...nel.org, 
	djwong@...nel.org, pavel@...nel.org, peterz@...radead.org, mingo@...hat.com, 
	will@...nel.org, boqun.feng@...il.com
Subject: Re: [PATCH v2 4/6] super: use a common iterator (Part 1)

On Sat 29-03-25 09:42:17, Christian Brauner wrote:
> Use a common iterator for all callbacks.
> 
> Signed-off-by: Christian Brauner <brauner@...nel.org>

Very nice! Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/super.c         | 67 +++++++++++-------------------------------------------
>  include/linux/fs.h |  6 ++++-
>  2 files changed, 18 insertions(+), 55 deletions(-)
> 
> diff --git a/fs/super.c b/fs/super.c
> index c67ea3cdda41..0dd208804a74 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -887,37 +887,7 @@ void drop_super_exclusive(struct super_block *sb)
>  }
>  EXPORT_SYMBOL(drop_super_exclusive);
>  
> -static void __iterate_supers(void (*f)(struct super_block *))
> -{
> -	struct super_block *sb, *p = NULL;
> -
> -	spin_lock(&sb_lock);
> -	list_for_each_entry(sb, &super_blocks, s_list) {
> -		if (super_flags(sb, SB_DYING))
> -			continue;
> -		sb->s_count++;
> -		spin_unlock(&sb_lock);
> -
> -		f(sb);
> -
> -		spin_lock(&sb_lock);
> -		if (p)
> -			__put_super(p);
> -		p = sb;
> -	}
> -	if (p)
> -		__put_super(p);
> -	spin_unlock(&sb_lock);
> -}
> -/**
> - *	iterate_supers - call function for all active superblocks
> - *	@f: function to call
> - *	@arg: argument to pass to it
> - *
> - *	Scans the superblock list and calls given function, passing it
> - *	locked superblock and given argument.
> - */
> -void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
> +void __iterate_supers(void (*f)(struct super_block *, void *), void *arg, bool excl)
>  {
>  	struct super_block *sb, *p = NULL;
>  
> @@ -927,14 +897,13 @@ void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
>  
>  		if (super_flags(sb, SB_DYING))
>  			continue;
> -
>  		sb->s_count++;
>  		spin_unlock(&sb_lock);
>  
> -		locked = super_lock_shared(sb);
> +		locked = super_lock(sb, excl);
>  		if (locked) {
>  			f(sb, arg);
> -			super_unlock_shared(sb);
> +			super_unlock(sb, excl);
>  		}
>  
>  		spin_lock(&sb_lock);
> @@ -1111,11 +1080,9 @@ int reconfigure_super(struct fs_context *fc)
>  	return retval;
>  }
>  
> -static void do_emergency_remount_callback(struct super_block *sb)
> +static void do_emergency_remount_callback(struct super_block *sb, void *unused)
>  {
> -	bool locked = super_lock_excl(sb);
> -
> -	if (locked && sb->s_root && sb->s_bdev && !sb_rdonly(sb)) {
> +	if (sb->s_bdev && !sb_rdonly(sb)) {
>  		struct fs_context *fc;
>  
>  		fc = fs_context_for_reconfigure(sb->s_root,
> @@ -1126,13 +1093,11 @@ static void do_emergency_remount_callback(struct super_block *sb)
>  			put_fs_context(fc);
>  		}
>  	}
> -	if (locked)
> -		super_unlock_excl(sb);
>  }
>  
>  static void do_emergency_remount(struct work_struct *work)
>  {
> -	__iterate_supers(do_emergency_remount_callback);
> +	__iterate_supers(do_emergency_remount_callback, NULL, true);
>  	kfree(work);
>  	printk("Emergency Remount complete\n");
>  }
> @@ -1148,24 +1113,18 @@ void emergency_remount(void)
>  	}
>  }
>  
> -static void do_thaw_all_callback(struct super_block *sb)
> +static void do_thaw_all_callback(struct super_block *sb, void *unused)
>  {
> -	bool locked = super_lock_excl(sb);
> -
> -	if (locked && sb->s_root) {
> -		if (IS_ENABLED(CONFIG_BLOCK))
> -			while (sb->s_bdev && !bdev_thaw(sb->s_bdev))
> -				pr_warn("Emergency Thaw on %pg\n", sb->s_bdev);
> -		thaw_super_locked(sb, FREEZE_HOLDER_USERSPACE);
> -		return;
> -	}
> -	if (locked)
> -		super_unlock_excl(sb);
> +	if (IS_ENABLED(CONFIG_BLOCK))
> +		while (sb->s_bdev && !bdev_thaw(sb->s_bdev))
> +			pr_warn("Emergency Thaw on %pg\n", sb->s_bdev);
> +	thaw_super_locked(sb, FREEZE_HOLDER_USERSPACE);
> +	return;
>  }
>  
>  static void do_thaw_all(struct work_struct *work)
>  {
> -	__iterate_supers(do_thaw_all_callback);
> +	__iterate_supers(do_thaw_all_callback, NULL, true);
>  	kfree(work);
>  	printk(KERN_WARNING "Emergency Thaw complete\n");
>  }
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 016b0fe1536e..0351500b71d2 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3515,7 +3515,11 @@ extern void put_filesystem(struct file_system_type *fs);
>  extern struct file_system_type *get_fs_type(const char *name);
>  extern void drop_super(struct super_block *sb);
>  extern void drop_super_exclusive(struct super_block *sb);
> -extern void iterate_supers(void (*)(struct super_block *, void *), void *);
> +void __iterate_supers(void (*f)(struct super_block *, void *), void *arg, bool excl);
> +static inline void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
> +{
> +	__iterate_supers(f, arg, false);
> +}
>  extern void iterate_supers_type(struct file_system_type *,
>  			        void (*)(struct super_block *, void *), void *);
>  
> 
> -- 
> 2.47.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR