linux-ext4 - Re: [PATCH RFC 2/8] btrfs: use super write guard in btrfs_reclaim_bgs

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Message-ID: <247c8075-60d3-4090-a76d-8d59d9e859ca@suse.com>
Date: Wed, 5 Nov 2025 07:12:38 +1030
From: Qu Wenruo <wqu@...e.com>
To: Christian Brauner <brauner@...nel.org>, linux-fsdevel@...r.kernel.org
Cc: Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
 linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org,
 linux-xfs@...r.kernel.org
Subject: Re: [PATCH RFC 2/8] btrfs: use super write guard in
 btrfs_reclaim_bgs_work()



在 2025/11/4 22:42, Christian Brauner 写道:
> Signed-off-by: Christian Brauner <brauner@...nel.org>
> ---
>   fs/btrfs/block-group.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
> index 5322ef2ae015..8284b9435758 100644
> --- a/fs/btrfs/block-group.c
> +++ b/fs/btrfs/block-group.c
> @@ -1850,7 +1850,7 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
>   	if (!btrfs_should_reclaim(fs_info))
>   		return;
>   
> -	sb_start_write(fs_info->sb);
> +	guard(super_write)(fs_info->sb);
>   
>   	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE)) {
>   		sb_end_write(fs_info->sb);

This one is still left using the old scheme, and there is another one in 
the mutex_trylock() branch.

I'm wondering how safe is the new scope based auto freeing.

Like when the freeing function is called? Will it break the existing 
freeing/locking sequence in other locations?

For this call site, sb_end_write() is always called last so it's fine.

Thanks,
Qu

> @@ -2030,7 +2030,6 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
>   	list_splice_tail(&retry_list, &fs_info->reclaim_bgs);
>   	spin_unlock(&fs_info->unused_bgs_lock);
>   	btrfs_exclop_finish(fs_info);
> -	sb_end_write(fs_info->sb);
>   }
>   
>   void btrfs_reclaim_bgs(struct btrfs_fs_info *fs_info)
>