Re: [f2fs-dev] [PATCH 2/4] f2fs: return early when trying to read null nid

[Jaegeuk Kim <jaegeuk@kernel.org>]

On Thu, Dec 24, 2015 at 01:49:24PM +0800, Chao Yu wrote:
> Hi Jaegeuk,
> 
> > -----Original Message-----
> > From: Jaegeuk Kim [mailto:jaegeuk@kernel.org]
> > Sent: Thursday, December 24, 2015 10:15 AM
> > To: linux-kernel@vger.kernel.org; linux-fsdevel@vger.kernel.org;
> > linux-f2fs-devel@lists.sourceforge.net
> > Cc: Jaegeuk Kim
> > Subject: [f2fs-dev] [PATCH 2/4] f2fs: return early when trying to read null nid
> > 
> > If get_node_page() gets zero nid, we can return early without getting a wrong
> > page. For example, get_dnode_of_data() can try to do that.
> 
> Good catch!
> 
> > 
> > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> > ---
> >  fs/f2fs/node.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> > index 341de5d..e17128d 100644
> > --- a/fs/f2fs/node.c
> > +++ b/fs/f2fs/node.c
> > @@ -1059,6 +1059,9 @@ struct page *get_node_page(struct f2fs_sb_info *sbi, pgoff_t nid)
> >  {
> >  	struct page *page;
> >  	int err;
> > +
> > +	if (!nid)
> > +		return ERR_PTR(-ENOENT);
> 
> How about expand to check upper and lower boundary:
> 
> 	if (check_nid_range)
> 		return ERR_PTR(-ENOENT);

It'd better to add f2fs_bug_on(check_nid_range()) after this.
Cause check_nid_range() checks its nid as *unlikely*, but this case seems
*likely*.

Thanks,

> 
> Thanks,
> 
> >  repeat:
> >  	page = grab_cache_page(NODE_MAPPING(sbi), nid);
> >  	if (!page)
> > --
> > 2.5.4 (Apple Git-61)
> > 
> > 
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