Re: [f2fs-dev] [PATCH 1/3] f2fs: check the page status filled from disk

From: Jaegeuk Kim <jaegeuk@kernel.org>
To: Chao Yu <chao2.yu@samsung.com>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 1/3] f2fs: check the page status filled from disk
Date: Tue, 5 Jan 2016 18:30:13 -0800	[thread overview]
Message-ID: <20160106023013.GA7016@jaegeuk.gateway> (raw)
In-Reply-To: <010101d14820$ad098290$071c87b0$@samsung.com>

Hi,

On Wed, Jan 06, 2016 at 09:21:29AM +0800, Chao Yu wrote:
> Hi Jaegeuk,
> 
> > -----Original Message-----
> > From: Jaegeuk Kim [mailto:jaegeuk@kernel.org]
> > Sent: Wednesday, January 06, 2016 1:49 AM
> > To: Chao Yu
> > Cc: linux-kernel@vger.kernel.org; linux-fsdevel@vger.kernel.org;
> > linux-f2fs-devel@lists.sourceforge.net
> > Subject: Re: [f2fs-dev] [PATCH 1/3] f2fs: check the page status filled from disk
> > 
> > Hi Chao,
> > 
> > On Tue, Jan 05, 2016 at 05:31:51PM +0800, Chao Yu wrote:
> > > Hi Jaegeuk,
> > >
> > > > -----Original Message-----
> > > > From: Jaegeuk Kim [mailto:jaegeuk@kernel.org]
> > > > Sent: Sunday, January 03, 2016 9:26 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 1/3] f2fs: check the page status filled from disk
> > > >
> > > > After reading a page, we need to check whether there is any error.
> > > >
> > > > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> > > > ---
> > > >  fs/f2fs/data.c | 8 ++++++++
> > > >  1 file changed, 8 insertions(+)
> > > >
> > > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > > > index 89a978c..11b2111 100644
> > > > --- a/fs/f2fs/data.c
> > > > +++ b/fs/f2fs/data.c
> > > > @@ -448,6 +448,14 @@ repeat:
> > > >
> > > >  		/* wait for read completion */
> > > >  		lock_page(page);
> > > > +		if (unlikely(!PageUptodate(page))) {
> > > > +			f2fs_put_page(page, 1);
> > > > +			return ERR_PTR(-EIO);
> > >
> > > There is a convention in get_new_data_page, anyway we should release ipage
> > > if there is any error occurs, but I think it will be ok to return directly
> > > since it seems impossible the new dentry page has its real block address.
> > 
> > Makes sense, but definitely ipage should be put. :)
> 
> Alright. :)
> 
> > 
> > >
> > > To avoid any bug here or wrong usage, how about add bug_on as following patch?
> > >
> > > >From d92f0f34493b27ef28da67c446d552ce721b5d6f Mon Sep 17 00:00:00 2001
> > > From: Chao Yu <chao2.yu@samsung.com>
> > > Date: Tue, 5 Jan 2016 15:28:56 +0800
> > > Subject: [PATCH] f2fs: add f2fs_bug_on in get_new_data_page
> > >
> > > In get_new_data_page, locked inode page should not be hold before
> > > get_read_data_page, this patch adds f2fs_bug_on to detect this
> > > condition.
> > >
> > > Signed-off-by: Chao Yu <chao2.yu@samsung.com>
> > > ---
> > >  fs/f2fs/data.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > >
> > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > > index 48f0bd3..2c5e3f6 100644
> > > --- a/fs/f2fs/data.c
> > > +++ b/fs/f2fs/data.c
> > > @@ -440,6 +440,8 @@ repeat:
> > >  		zero_user_segment(page, 0, PAGE_CACHE_SIZE);
> > >  		SetPageUptodate(page);
> > >  	} else {
> > > +		f2fs_bug_on(F2FS_I_SB(inode), ipage);
> > > +
> > >  		f2fs_put_page(page, 1);
> > >
> > >  		page = get_read_data_page(inode, index, READ_SYNC, true);
> > > --
> > > 2.6.3
> > >
> > >
> > > > +		}
> > > > +		if (unlikely(page->mapping != mapping)) {
> > > > +			f2fs_put_page(page, 1);
> > > > +			goto repeat;
> > > > +		}
> > >
> > > How about use get_lock_data_page to avoid duplicated code?
> > 
> > Agreed.
> > 
> > How about this?
> > 
> > From fef77fb244a706491e8e4c46cb245e99e22003c3 Mon Sep 17 00:00:00 2001
> > From: Jaegeuk Kim <jaegeuk@kernel.org>
> > Date: Fri, 1 Jan 2016 22:03:47 -0800
> > Subject: [PATCH] f2fs: check the page status filled from disk
> > 
> > After reading a page, we need to check whether there is any error.
> > 
> > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> > ---
> >  fs/f2fs/data.c | 14 +++++++++-----
> >  1 file changed, 9 insertions(+), 5 deletions(-)
> > 
> > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > index 89a978c..89d633a 100644
> > --- a/fs/f2fs/data.c
> > +++ b/fs/f2fs/data.c
> > @@ -442,12 +442,16 @@ repeat:
> >  	} else {
> >  		f2fs_put_page(page, 1);
> > 
> > -		page = get_read_data_page(inode, index, READ_SYNC, true);
> > -		if (IS_ERR(page))
> > -			goto repeat;
> > +		f2fs_bug_on(F2FS_I_SB(inode), ipage);
> > 
> > -		/* wait for read completion */
> > -		lock_page(page);
> > +		page = get_lock_data_page(inode, index, true);
> > +		if (IS_ERR(page)) {
> > +			if (PTR_ERR(page) == -EIO) {
> > +				f2fs_put_page(ipage, 1);
> > +				return page;
> > +			}
> > +			goto repeat;
> 
> Seems if get_lock_data_page always return -EFAULT, we may run into an
> infinite loop. IMO, it's not a bad thing to tolerate other error more
> than EIO returned from get_lock_data_page. How about return directly
> when error is returned? And add a bug_on for ENOENT which seems not
> impossible here?

Hmm. I can only expect EIO, ENOMEM, and ENOENT.
What condition can we get EFAULT?

Thanks,

> 
> Thanks,
> 
> > +		}
> >  	}
> >  got_it:
> >  	if (new_i_size && i_size_read(inode) <
> > --
> > 2.6.3
> 