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From:   Zhouyi Zhou <zhouzhouyi@gmail.com>
Date:   Sat, 11 Apr 2020 11:09:59 +0800
Message-ID: <CAABZP2yNZoSGr+t6T6KdFhu_3xM1HsM_ft1rK=gHRyyRTbCUMw@mail.gmail.com>
Subject: ping: [PATCH v3] NFS:remove redundant call to nfs_do_access
To:     trond.myklebust@hammerspace.com, anna.schumaker@netapp.com,
        linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org,
        paulmck@linux.ibm.com, paulmck@linux.vnet.ibm.com, neilb@suse.com
Cc:     Zhouyi Zhou <zhouzhouyi@gmail.com>, 340442286 <340442286@qq.com>
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Sender: linux-nfs-owner@vger.kernel.org
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ping

On 3/6/20, Zhouyi Zhou <zhouzhouyi@gmail.com> wrote:
> In function nfs_permission:
> 1. the rcu_read_lock and rcu_read_unlock around nfs_do_access
> is unnecessary because the rcu critical data structure is already
> protected in subsidiary function nfs_access_get_cached_rcu. No other
> data structure needs rcu_read_lock in nfs_do_access.
>
> 2. call nfs_do_access once is enough, because:
> 2-1. when mask has MAY_NOT_BLOCK bit
> The second call to nfs_do_access will not happen.
>
> 2-2. when mask has no MAY_NOT_BLOCK bit
> The second call to nfs_do_access will happen if res == -ECHILD, which
> means the first nfs_do_access goes out after statement if (!may_block).
> The second call to nfs_do_access will go through this procedure once
> again except continue the work after if (!may_block).
> But above work can be performed by only one call to nfs_do_access
> without mangling the mask flag.
>
> Tested in x86_64
> Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
> ---
>  fs/nfs/dir.c |    9 +--------
>  1 files changed, 1 insertions(+), 8 deletions(-)
>
> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> index 193d6fb..37b0c10 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -2732,14 +2732,7 @@ int nfs_permission(struct inode *inode, int mask)
>  	if (!NFS_PROTO(inode)->access)
>  		goto out_notsup;
>
> -	/* Always try fast lookups first */
> -	rcu_read_lock();
> -	res = nfs_do_access(inode, cred, mask|MAY_NOT_BLOCK);
> -	rcu_read_unlock();
> -	if (res == -ECHILD && !(mask & MAY_NOT_BLOCK)) {
> -		/* Fast lookup failed, try the slow way */
> -		res = nfs_do_access(inode, cred, mask);
> -	}
> +	res = nfs_do_access(inode, cred, mask);
>  out:
>  	if (!res && (mask & MAY_EXEC))
>  		res = nfs_execute_ok(inode, mask);
> --
> 1.7.1
>
>