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

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Date:	Fri, 25 Dec 2015 08:57:19 +0800
From:	Chao Yu <chao2.yu@...sung.com>
To:	'Jaegeuk Kim' <jaegeuk@...nel.org>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net
Subject: RE: [f2fs-dev] [PATCH 2/4] f2fs: return early when trying to read null
 nid

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk@...nel.org]
> Sent: Friday, December 25, 2015 4:16 AM
> To: Chao Yu
> Cc: linux-kernel@...r.kernel.org; linux-fsdevel@...r.kernel.org;
> linux-f2fs-devel@...ts.sourceforge.net
> Subject: Re: [f2fs-dev] [PATCH 2/4] f2fs: return early when trying to read null nid
> 
> On Thu, Dec 24, 2015 at 01:49:24PM +0800, Chao Yu wrote:
> > Hi Jaegeuk,
> >
> > > -----Original Message-----
> > > From: Jaegeuk Kim [mailto:jaegeuk@...nel.org]
> > > Sent: Thursday, December 24, 2015 10:15 AM
> > > To: linux-kernel@...r.kernel.org; linux-fsdevel@...r.kernel.org;
> > > linux-f2fs-devel@...ts.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@...nel.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*.

Agreed.

Thanks,

> 
> Thanks,
> 
> >
> > Thanks,
> >
> > >  repeat:
> > >  	page = grab_cache_page(NODE_MAPPING(sbi), nid);
> > >  	if (!page)
> > > --
> > > 2.5.4 (Apple Git-61)
> > >
> > >
> > > ------------------------------------------------------------------------------
> > > _______________________________________________
> > > Linux-f2fs-devel mailing list
> > > Linux-f2fs-devel@...ts.sourceforge.net
> > > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel

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