linux-kernel - Re: [PATCH] NFS: Correct timing for assigning access cache timestamp

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Message-ID: <84E89457-478E-42F8-AC5F-DFFC58FBEFFB@hammerspace.com>
Date:   Tue, 14 Mar 2023 18:51:24 +0000
From:   Trond Myklebust <trondmy@...merspace.com>
To:     Chengen Du <chengen.du@...onical.com>
CC:     Anna Schumaker <anna@...nel.org>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] NFS: Correct timing for assigning access cache timestamp



> On Mar 8, 2023, at 03:03, Chengen Du <chengen.du@...onical.com> wrote:
> 
> When the user's login time is newer than the cache's timestamp,
> the original entry in the RB-tree will be replaced by a new entry.
> Currently, the timestamp is only set if the entry is not found in
> the RB-tree, which can cause the timestamp to be undefined when
> the entry exists. This may result in a significant increase in
> ACCESS operations if the timestamp is set to zero.
> 
> Signed-off-by: Chengen Du <chengen.du@...onical.com>
> ---
> fs/nfs/dir.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> index a41c3ee4549c..6fbcbb8d6587 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -3089,7 +3089,6 @@ static void nfs_access_add_rbtree(struct inode *inode,
> else
> goto found;
> }
> - set->timestamp = ktime_get_ns();
> rb_link_node(&set->rb_node, parent, p);
> rb_insert_color(&set->rb_node, root_node);
> list_add_tail(&set->lru, &nfsi->access_cache_entry_lru);
> @@ -3114,6 +3113,7 @@ void nfs_access_add_cache(struct inode *inode, struct nfs_access_entry *set,
> cache->fsgid = cred->fsgid;
> cache->group_info = get_group_info(cred->group_info);
> cache->mask = set->mask;
> + cache->timestamp = ktime_get_ns();
> 
> /* The above field assignments must be visible
> * before this item appears on the lru.  We cannot easily
> -- 
> 2.37.2
> 

Doh! Nice catch…

Anna, please pick this up for 6.2-rcX and add an appropriate

Fixes: 0eb43812c027 ("NFS: Clear the file access cache upon login”)

Thanks!
  Trond

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