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From:   Zhouyi Zhou <zhouzhouyi@gmail.com>
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>
Subject: [PATCH v3] NFS:remove redundant call to nfs_do_access
Date:   Fri,  6 Mar 2020 03:45:26 +0000
Message-Id: <1583466326-27867-1-git-send-email-zhouzhouyi@gmail.com>
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk

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