linux-kernel - Re: [PATCH] f2fs: fix fdatasync

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Message-ID: <20161117034138.GA69766@jaegeuk>
Date:   Wed, 16 Nov 2016 19:41:38 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, chao@...nel.org
Subject: Re: [PATCH] f2fs: fix fdatasync

On Thu, Nov 17, 2016 at 11:35:58AM +0800, Chao Yu wrote:
> On 2016/11/17 10:59, Jaegeuk Kim wrote:
> > On Thu, Nov 17, 2016 at 10:51:37AM +0800, Chao Yu wrote:
> >> Hi Jaegeuk,
> >>
> >> On 2016/11/17 3:13, Jaegeuk Kim wrote:
> >>> Hi Chao,
> >>>
> >>> On Wed, Nov 16, 2016 at 08:12:11PM +0800, Chao Yu wrote:
> >>>> For below two cases, we can't guarantee data consistence:
> >>>>
> >>>> a)
> >>>> 1. xfs_io "pwrite 0 4195328" "fsync"
> >>>> 2. xfs_io "pwrite 4195328 1024" "fdatasync"
> >>>> 3. godown
> >>>> 4. umount & mount
> >>>> --> isize we updated before fdatasync won't be recovered
> >>>>
> >>>> b)
> >>>> 1. xfs_io "pwrite -S 0xcc 0 4202496" "fsync"
> >>>> 2. xfs_io "fpunch 4194304 4096" "fdatasync"
> >>>> 3. godown
> >>>> 4. umount & mount
> >>>> --> dnode we punched before fdatasync won't be recovered
> >>>>
> >>>> The reason is that normally fdatasync won't be aware of modification
> >>>> of metadata in file, e.g. isize changing, dnode updating, so in ->fsync
> >>>> we will skip flushing node pages for above cases, result in making
> >>>> fdatasynced file being lost during recovery.
> >>>>
> >>>> Introduce FDATASYNC_INO global ino cache for tracking node changing,
> >>>> later fdatasync choose to flush nodes depend on ino cache state.
> >>>
> >>> We don't need to add this additionally, and would be better to consider other
> >>> major metadata as well.
> >>>
> >>> How about this?
> >>
> >> Seems it can't track file after evict?
> > 
> > Do we need that? That means inode page was already up-to-date?
> 
> I mean if node/data page of inode were writeback by kworker, after evict, if
> user open it again and call fdatasync, after sudden power-off, we will not
> recover it.

That will be handled by need_inode_block_update() below?

Thanks,