linux-kernel - Re: [PATCH 2/2] fs: nfs: dir.c: Fix sparse error

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Date:   Fri, 6 Dec 2019 11:00:02 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     madhuparnabhowmik04@...il.com
Cc:     trond.myklebust@...merspace.com, anna.schumaker@...app.com,
        linux-nfs@...r.kernel.org, rcu@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-kernel@...r.kernel.org, paulmck@...nel.org
Subject: Re: [PATCH 2/2] fs: nfs: dir.c: Fix sparse error

+Paul, here is the dependent patch for the list_prev_rcu() patch Madhuparna
posted.

On Fri, Dec 06, 2019 at 08:46:40PM +0530, madhuparnabhowmik04@...il.com wrote:
> From: Madhuparna Bhowmik <madhuparnabhowmik04@...il.com>
> 
> This patch fixes the following errors:
> fs/nfs/dir.c:2353:14: error: incompatible types in comparison expression (different address spaces):
> fs/nfs/dir.c:2353:14:    struct list_head [noderef] <asn:4> *
> fs/nfs/dir.c:2353:14:    struct list_head *
> 
> caused due to directly accessing the prev pointer of
> a RCU protected list.
> Accessing the pointer using the macro list_prev_rcu() fixes this error.
> 
> Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik04@...il.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 e180033e35cf..2035254cc283 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -2350,7 +2350,7 @@ static int nfs_access_get_cached_rcu(struct inode *inode, const struct cred *cre
>  	rcu_read_lock();
>  	if (nfsi->cache_validity & NFS_INO_INVALID_ACCESS)
>  		goto out;
> -	lh = rcu_dereference(nfsi->access_cache_entry_lru.prev);
> +	lh = rcu_dereference(list_prev_rcu(&nfsi->access_cache_entry_lru));
>  	cache = list_entry(lh, struct nfs_access_entry, lru);
>  	if (lh == &nfsi->access_cache_entry_lru ||
>  	    cred != cache->cred)
> -- 
> 2.17.1
>