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Message-ID: <ef3bedaf187e9133af616997a7bc85b5a73a8aa3.camel@kernel.org>
Subject: Re: [PATCH stable 6.6 and 6.7] NFS: Fix data corruption caused by
 congestion.
From: Jeff Layton <jlayton@kernel.org>
To: NeilBrown <neilb@suse.de>, stable@vger.kernel.org, Trond Myklebust
	 <trond.myklebust@hammerspace.com>, Anna Schumaker <anna@kernel.org>
Cc: linux-nfs@vger.kernel.org, Dan Aloni <dan.aloni@vastdata.com>
Date: Wed, 06 Mar 2024 12:12:44 -0500
In-Reply-To: <cfec488eccfc3469d18dd94b05a00919cc152113.camel@kernel.org>
References: <170907621128.24797.4390391329078744015@noble.neil.brown.name>
	 <cfec488eccfc3469d18dd94b05a00919cc152113.camel@kernel.org>
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On Wed, 2024-03-06 at 08:42 -0500, Jeff Layton wrote:
> On Wed, 2024-02-28 at 10:23 +1100, NeilBrown wrote:
> > when AOP_WRITEPAGE_ACTIVATE is returned (as NFS does when it detects
> > congestion) it is important that the folio is redirtied.
> > nfs_writepage_locked() doesn't do this, so files can become corrupted a=
s
> > writes can be lost.
> >=20
> > Note that this is not needed in v6.8 as AOP_WRITEPAGE_ACTIVATE cannot b=
e
> > returned.  It is needed for kernels v5.18..v6.7.  Prior to 6.3 the patc=
h
> > is different as it needs to mention "page", not "folio".
> >=20
>=20
> Neil, I have a question about the above statement. In Linus's tree as of
> this morning (v6.8-rc7-ish), it does this in nfs_writepages_locked:
>=20
>         if (wbc->sync_mode =3D=3D WB_SYNC_NONE &&
>             NFS_SERVER(inode)->write_congested)          =20
>                 return AOP_WRITEPAGE_ACTIVATE;
>=20

Sorry, I meant to say:

The only caller of nfs_writepages_locked is nfs_wb_folio, and I don't
see where it redirties the folio. Why don't we need this in v6.8?


>=20
> > Reported-and-tested-by: Jacek Tomaka <Jacek.Tomaka@poczta.fm>
> > Fixes: 6df25e58532b ("nfs: remove reliance on bdi congestion")
> > Signed-off-by: NeilBrown <neilb@suse.de>
> > ---
> >  fs/nfs/write.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >=20
> > diff --git a/fs/nfs/write.c b/fs/nfs/write.c
> > index b664caea8b4e..9e345d3c305a 100644
> > --- a/fs/nfs/write.c
> > +++ b/fs/nfs/write.c
> > @@ -668,8 +668,10 @@ static int nfs_writepage_locked(struct folio *foli=
o,
> >  	int err;
> > =20
> >  	if (wbc->sync_mode =3D=3D WB_SYNC_NONE &&
> > -	    NFS_SERVER(inode)->write_congested)
> > +	    NFS_SERVER(inode)->write_congested) {
> > +		folio_redirty_for_writepage(wbc, folio);
> >  		return AOP_WRITEPAGE_ACTIVATE;
> > +	}
> > =20
> >  	nfs_inc_stats(inode, NFSIOS_VFSWRITEPAGE);
> >  	nfs_pageio_init_write(&pgio, inode, 0, false,
>=20

--=20
Jeff Layton <jlayton@kernel.org>