linux-kernel - Re: [PATCH 1/2] erofs: clean up z_erofs_extent

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Date:   Fri, 11 Mar 2022 15:28:28 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     Yue Hu <zbestahu@...il.com>
Cc:     linux-erofs@...ts.ozlabs.org, Chao Yu <chao@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, zhangwen@...lpad.com,
        huyue2@...lpad.com
Subject: Re: [PATCH 1/2] erofs: clean up z_erofs_extent_lookback

On Fri, Mar 11, 2022 at 03:12:32PM +0800, Yue Hu wrote:
> On Fri, 11 Mar 2022 02:27:42 +0800
> Gao Xiang <hsiangkao@...ux.alibaba.com> wrote:
> 
> > Avoid the unnecessary tail recursion since it can be converted into
> > a loop directly in order to prevent potential stack overflow.
> > 
> > It's a pretty straightforward conversion.
> > 
> > Signed-off-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
> > ---
> >  fs/erofs/zmap.c | 67 ++++++++++++++++++++++++-------------------------
> >  1 file changed, 33 insertions(+), 34 deletions(-)
> > 
> > diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
> > index b4059b9c3bac..572f0b8151ba 100644
> > --- a/fs/erofs/zmap.c
> > +++ b/fs/erofs/zmap.c
> > @@ -431,48 +431,47 @@ static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,
> >  				   unsigned int lookback_distance)
> >  {
> >  	struct erofs_inode *const vi = EROFS_I(m->inode);
> > -	struct erofs_map_blocks *const map = m->map;
> >  	const unsigned int lclusterbits = vi->z_logical_clusterbits;
> > -	unsigned long lcn = m->lcn;
> > -	int err;
> >  
> > -	if (lcn < lookback_distance) {
> > -		erofs_err(m->inode->i_sb,
> > -			  "bogus lookback distance @ nid %llu", vi->nid);
> > -		DBG_BUGON(1);
> > -		return -EFSCORRUPTED;
> > -	}
> > +	while (m->lcn >= lookback_distance) {
> > +		unsigned long lcn = m->lcn - lookback_distance;
> > +		int err;
> 
> may better to declare variable 'lclusterbits' in loop just like 'err' usage?

I'm fine with either way. Ok, will post the next version later.

Thanks,
Gao Xiang