linux-kernel - Re: [PATCH v6 1/4] cramfs: direct memory access support

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Message-ID: <nycvar.YSQ.7.76.1710131332360.1718@knanqh.ubzr>
Date:   Fri, 13 Oct 2017 13:39:13 -0400 (EDT)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Al Viro <viro@...IV.linux.org.uk>
cc:     Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-embedded@...r.kernel.org, linux-kernel@...r.kernel.org,
        Chris Brandt <Chris.Brandt@...esas.com>
Subject: Re: [PATCH v6 1/4] cramfs: direct memory access support

On Fri, 13 Oct 2017, Al Viro wrote:

> On Thu, Oct 12, 2017 at 02:16:10AM -0400, Nicolas Pitre wrote:
> 
> >  static void cramfs_kill_sb(struct super_block *sb)
> >  {
> >  	struct cramfs_sb_info *sbi = CRAMFS_SB(sb);
> >  
> > -	kill_block_super(sb);
> > +	if (IS_ENABLED(CCONFIG_CRAMFS_MTD)) {
> > +		if (sbi->mtd_point_size)
> > +			mtd_unpoint(sb->s_mtd, 0, sbi->mtd_point_size);
> > +		if (sb->s_mtd)
> > +			kill_mtd_super(sb);
> 
> ...
> 
> > +	mtd_unpoint(sb->s_mtd, 0, PAGE_SIZE);
> > +	err = mtd_point(sb->s_mtd, 0, sbi->size, &sbi->mtd_point_size,
> > +			&sbi->linear_virt_addr, &sbi->linear_phys_addr);
> > +	if (err || sbi->mtd_point_size != sbi->size) {
> 
> What happens if that mtd_point() fails?  Note that ->kill_sb() will be
> called anyway and ->mtd_point_size is going to be non-zero here...

mtd_point() always clears sbi->mtd_point_size first thing upon entry 
even before it has a chance to fail. So it it fails then 
sbi->mtd_point_size will be zero and ->kill_sb() will skip the unpoint 
call.


Nicolas