linux-kernel - Re: [PATCH v4] f2fs: add sysfs nodes to get runtime compression stat

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Message-ID: <YEt00vJ6oVfoRjSJ@kroah.com>
Date:   Fri, 12 Mar 2021 15:04:02 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Daeho Jeong <daeho43@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, kernel-team@...roid.com,
        Daeho Jeong <daehojeong@...gle.com>
Subject: Re: [PATCH v4] f2fs: add sysfs nodes to get runtime compression stat

On Fri, Mar 12, 2021 at 10:56:13PM +0900, Daeho Jeong wrote:
> Thanks for suggesting me sysfs_emit().
> 
> For atomic values, actually, those are needed for writer part, not reader.
> 
> +#define add_compr_block_stat(inode, blocks)                            \
> +       do {                                                            \
> +               struct f2fs_sb_info *sbi = F2FS_I_SB(inode);            \
> +               int diff = F2FS_I(inode)->i_cluster_size - blocks;      \
> +               atomic64_add(blocks, &sbi->compr_written_block);        \
> +               atomic64_add(diff, &sbi->compr_saved_block);            \
> +       } while (0)
> 
> I needed a protection here, because they might be updated in the race condition.

Why?  What are you trying to protect from "racing" here?

thanks,

greg k-h