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Date:   Tue, 22 Dec 2020 16:20:27 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Vivek Goyal <vgoyal@redhat.com>
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-unionfs@vger.kernel.org, jlayton@kernel.org,
        amir73il@gmail.com, sargun@sargun.me, miklos@szeredi.hu,
        jack@suse.cz, neilb@suse.com, viro@zeniv.linux.org.uk, hch@lst.de
Subject: Re: [PATCH 3/3] overlayfs: Report writeback errors on upper
Message-ID: <20201222162027.GJ874@casper.infradead.org>
References: <20201221195055.35295-1-vgoyal@redhat.com>
 <20201221195055.35295-4-vgoyal@redhat.com>
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On Mon, Dec 21, 2020 at 02:50:55PM -0500, Vivek Goyal wrote:
> +static int ovl_errseq_check_advance(struct super_block *sb, struct file *file)
> +{
> +	struct ovl_fs *ofs = sb->s_fs_info;
> +	struct super_block *upper_sb;
> +	int ret;
> +
> +	if (!ovl_upper_mnt(ofs))
> +		return 0;
> +
> +	upper_sb = ovl_upper_mnt(ofs)->mnt_sb;
> +
> +	if (!errseq_check(&upper_sb->s_wb_err, file->f_sb_err))
> +		return 0;
> +
> +	/* Something changed, must use slow path */
> +	spin_lock(&file->f_lock);
> +	ret = errseq_check_and_advance(&upper_sb->s_wb_err, &file->f_sb_err);
> +	spin_unlock(&file->f_lock);

Why are you microoptimising syncfs()?  Are there really applications which
call syncfs() in a massively parallel manner on the same file descriptor?