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Message-ID: <dc5d464d14d45f7df932c1b53d95c84b4f5bbcc3.camel@gmail.com>
Subject: Re: [PATCH] NFS: Judge the file access cache's timestamp in rcu path
From:   Trond Myklebust <trondmy@gmail.com>
To:     Chengen Du <chengen.du@canonical.com>,
        trond.myklebust@hammerspace.com
Cc:     anna@kernel.org, linux-nfs@vger.kernel.org,
        linux-kernel@vger.kernel.org
Date:   Wed, 11 Jan 2023 21:48:13 -0500
In-Reply-To: <CAPza5qc03KLCWJ5u=yFZ3wtKBDHBNvSM44xOTt2AGd9PoRs0Ow@mail.gmail.com>
References: <20221230030432.38908-1-chengen.du@canonical.com>
         <CAPza5qc03KLCWJ5u=yFZ3wtKBDHBNvSM44xOTt2AGd9PoRs0Ow@mail.gmail.com>
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On Thu, 2023-01-12 at 09:26 +0800, Chengen Du wrote:
> Hi,
>=20
> The patch follows the commit 0eb43812c027 but handles the stale cache
> in rcu path.
> The stale cache will remain in the list's tail if no other users
> operate on that inode.
> May I ask if this patch has any other concerns or drawbacks that need
> to be considered?
>=20
> Best regards,
> Chengen Du

No complaints. The patch has already been merged into 6.2-rc3.

Thanks!
  Trond

>=20
> On Fri, Dec 30, 2022 at 11:05 AM Chengen Du
> <chengen.du@canonical.com> wrote:
> >=20
> > If the user's login time is newer than the cache's timestamp,
> > we expect the cache may be stale and need to clear.
> > The stale cache will remain in the list's tail if no other
> > users operate on that inode.
> > Once the user accesses the inode, the stale cache will be
> > returned in rcu path.
> >=20
> > Signed-off-by: Chengen Du <chengen.du@canonical.com>
> > ---
> > =C2=A0fs/nfs/dir.c | 3 +++
> > =C2=A01 file changed, 3 insertions(+)
> >=20
> > diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> > index ea1ceffa1d3a..d490d64a9ebd 100644
> > --- a/fs/nfs/dir.c
> > +++ b/fs/nfs/dir.c
> > @@ -3023,6 +3023,7 @@ static int nfs_access_get_cached_rcu(struct
> > inode *inode, const struct cred *cre
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * but do it without lo=
cking.
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct nfs_inode *nfsi =3D N=
FS_I(inode);
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 u64 login_time =3D nfs_access_log=
in_time(current, cred);
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct nfs_access_entry *cac=
he;
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 int err =3D -ECHILD;
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct list_head *lh;
> > @@ -3037,6 +3038,8 @@ static int nfs_access_get_cached_rcu(struct
> > inode *inode, const struct cred *cre
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0 cache =3D NULL;
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (cache =3D=3D NULL)
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0 goto out;
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if ((s64)(login_time - cache->tim=
estamp) > 0)
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0 goto out;
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (nfs_check_cache_invalid(=
inode, NFS_INO_INVALID_ACCESS))
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0 goto out;
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 *mask =3D cache->mask;
> > --
> > 2.37.2
> >=20

--=20
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com