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From:   NeilBrown <neilb@suse.de>
To:     Zhouyi Zhou <zhouzhouyi@gmail.com>,
        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
Date:   Sat, 11 Apr 2020 14:10:30 +1000
Cc:     Zhouyi Zhou <zhouzhouyi@gmail.com>, 340442286 <340442286@qq.com>
Subject: Re: ping: [PATCH v3] NFS:remove redundant call to nfs_do_access
In-Reply-To: <CAABZP2yNZoSGr+t6T6KdFhu_3xM1HsM_ft1rK=gHRyyRTbCUMw@mail.gmail.com>
References: <CAABZP2yNZoSGr+t6T6KdFhu_3xM1HsM_ft1rK=gHRyyRTbCUMw@mail.gmail.com>
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On Sat, Apr 11 2020, Zhouyi Zhou wrote:

> ping

You patch has landed in Linux.

Commit eb095c14030f ("NFS:remove redundant call to nfs_do_access")

Thanks,
NeilBrown

>
> 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
>>
>>

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