linux-kernel - Re: [PATCH] NFS: Judge the file access cache's timestamp in rcu path

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Date:   Wed, 11 Jan 2023 21:48:13 -0500
From:   Trond Myklebust <trondmy@...il.com>
To:     Chengen Du <chengen.du@...onical.com>,
        trond.myklebust@...merspace.com
Cc:     anna@...nel.org, linux-nfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] NFS: Judge the file access cache's timestamp in rcu path

On Thu, 2023-01-12 at 09:26 +0800, Chengen Du wrote:
> Hi,
> 
> 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?
> 
> Best regards,
> Chengen Du

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

Thanks!
  Trond

> 
> On Fri, Dec 30, 2022 at 11:05 AM Chengen Du
> <chengen.du@...onical.com> wrote:
> > 
> > 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.
> > 
> > Signed-off-by: Chengen Du <chengen.du@...onical.com>
> > ---
> >  fs/nfs/dir.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > 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
> >          * but do it without locking.
> >          */
> >         struct nfs_inode *nfsi = NFS_I(inode);
> > +       u64 login_time = nfs_access_login_time(current, cred);
> >         struct nfs_access_entry *cache;
> >         int err = -ECHILD;
> >         struct list_head *lh;
> > @@ -3037,6 +3038,8 @@ static int nfs_access_get_cached_rcu(struct
> > inode *inode, const struct cred *cre
> >                 cache = NULL;
> >         if (cache == NULL)
> >                 goto out;
> > +       if ((s64)(login_time - cache->timestamp) > 0)
> > +               goto out;
> >         if (nfs_check_cache_invalid(inode, NFS_INO_INVALID_ACCESS))
> >                 goto out;
> >         *mask = cache->mask;
> > --
> > 2.37.2
> > 

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@...merspace.com