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From: Trond Myklebust <trond.myklebust@primarydata.com>
To: Jeff Layton <jeff.layton@primarydata.com>
Cc: Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
	Peng Tao <tao.peng@primarydata.com>
Subject: Re: [PATCH v3 1/5] NFSv4: Ensure we reference the inode for return-on-close in delegreturn
Date: Fri, 6 Feb 2015 08:35:31 -0500	[thread overview]
Message-ID: <CAHQdGtRiTE0gWnfkrKaV==65TjkymgYUqSzJOMmQO_LFas6GPg@mail.gmail.com> (raw)
In-Reply-To: <CAHQdGtQR4xc4Dge_nktpWO9reb=wDMiWk1drcEj6kDKQJVRdSQ@mail.gmail.com>

On Fri, Feb 6, 2015 at 8:31 AM, Trond Myklebust
<trond.myklebust@primarydata.com> wrote:
> On Fri, Feb 6, 2015 at 7:26 AM, Jeff Layton <jeff.layton@primarydata.com> wrote:
>> On Thu,  5 Feb 2015 23:45:03 -0500
>> Trond Myklebust <trond.myklebust@primarydata.com> wrote:
>>
>>> If we have to do a return-on-close in the delegreturn code, then
>>> we must ensure that the inode and super block remain referenced.
>>>
>>> Cc: Peng Tao <tao.peng@primarydata.com>
>>> Cc: stable@vger.kernel.org # 3.17.x
>>> Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
>>> Reviewed-by: Peng Tao <tao.peng@primarydata.com>
>>> ---
>>>  fs/nfs/internal.h | 22 +++++++++++++++++++++-
>>>  fs/nfs/nfs4proc.c | 14 +++++++++-----
>>>  fs/nfs/super.c    |  9 ++++++---
>>>  3 files changed, 36 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
>>> index a98cf2006179..21469e6e3834 100644
>>> --- a/fs/nfs/internal.h
>>> +++ b/fs/nfs/internal.h
>>> @@ -391,7 +391,7 @@ extern struct rpc_stat nfs_rpcstat;
>>>
>>>  extern int __init register_nfs_fs(void);
>>>  extern void __exit unregister_nfs_fs(void);
>>> -extern void nfs_sb_active(struct super_block *sb);
>>> +extern bool nfs_sb_active(struct super_block *sb);
>>>  extern void nfs_sb_deactive(struct super_block *sb);
>>>
>>>  /* namespace.c */
>>> @@ -514,6 +514,26 @@ extern int nfs41_walk_client_list(struct nfs_client *clp,
>>>                               struct nfs_client **result,
>>>                               struct rpc_cred *cred);
>>>
>>> +static inline struct inode *nfs_igrab_and_active(struct inode *inode)
>>> +{
>>> +     inode = igrab(inode);
>>
>> I would expect that you already hold a reference to the inode so
>> shouldn't that never return NULL? If so, then you could use ihold()
>> instead and simplify this a little.
>
> The choice of igrab() is deliberate here because we may be called in
> situations where the inode is in the process of being freed. Both
> delegreturn and layoutreturn can be called as part of an 'evict_inode'
> callback.

Just to clarify; the calls in evict_inode are safe, because we no
longer apply the asynchronous flag in the '!sync' case, however it
would still be bad to call ihold()+iput() in that situation.

>>
>>> +     if (inode != NULL && !nfs_sb_active(inode->i_sb)) {
>>> +             iput(inode);
>>> +             inode = NULL;
>>> +     }
>>> +     return inode;
>>> +}
>>> +
>>> +static inline void nfs_iput_and_deactive(struct inode *inode)
>>> +{
>>> +     if (inode != NULL) {
>>> +             struct super_block *sb = inode->i_sb;
>>> +
>>> +             iput(inode);
>>> +             nfs_sb_deactive(sb);
>>> +     }
>>> +}
>>> +
>>>  /*
>>>   * Determine the device name as a string
>>>   */
>>> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
>>> index cd4295d84d54..dd892a4e7eb3 100644
>>> --- a/fs/nfs/nfs4proc.c
>>> +++ b/fs/nfs/nfs4proc.c
>>> @@ -5175,9 +5175,13 @@ static void nfs4_delegreturn_done(struct rpc_task *task, void *calldata)
>>>  static void nfs4_delegreturn_release(void *calldata)
>>>  {
>>>       struct nfs4_delegreturndata *data = calldata;
>>> +     struct inode *inode = data->inode;
>>>
>>> -     if (data->roc)
>>> -             pnfs_roc_release(data->inode);
>>> +     if (inode) {
>>> +             if (data->roc)
>>> +                     pnfs_roc_release(inode);
>>> +             nfs_iput_and_deactive(inode);
>>> +     }
>>>       kfree(calldata);
>>>  }
>>>
>>> @@ -5234,9 +5238,9 @@ static int _nfs4_proc_delegreturn(struct inode *inode, struct rpc_cred *cred, co
>>>       nfs_fattr_init(data->res.fattr);
>>>       data->timestamp = jiffies;
>>>       data->rpc_status = 0;
>>> -     data->inode = inode;
>>> -     data->roc = list_empty(&NFS_I(inode)->open_files) ?
>>> -                 pnfs_roc(inode) : false;
>>> +     data->inode = nfs_igrab_and_active(inode);
>>> +     if (data->inode)
>>> +             data->roc = nfs4_roc(inode);
>>>
>>>       task_setup_data.callback_data = data;
>>>       msg.rpc_argp = &data->args;
>>> diff --git a/fs/nfs/super.c b/fs/nfs/super.c
>>> index 31a11b0e885d..368d9395d2e7 100644
>>> --- a/fs/nfs/super.c
>>> +++ b/fs/nfs/super.c
>>> @@ -405,12 +405,15 @@ void __exit unregister_nfs_fs(void)
>>>       unregister_filesystem(&nfs_fs_type);
>>>  }
>>>
>>> -void nfs_sb_active(struct super_block *sb)
>>> +bool nfs_sb_active(struct super_block *sb)
>>>  {
>>>       struct nfs_server *server = NFS_SB(sb);
>>>
>>> -     if (atomic_inc_return(&server->active) == 1)
>>> -             atomic_inc(&sb->s_active);
>>> +     if (!atomic_inc_not_zero(&sb->s_active))
>>> +             return false;
>>> +     if (atomic_inc_return(&server->active) != 1)
>>> +             atomic_dec(&sb->s_active);
>>
>> Could you end up doing a 1->0 s_active transition here? Shouldn't this
>> be a deactivate_super instead?
>
> No. The above line ensures that we take 1 reference to sb->s_active
> (when server->active does a 0->1 transition) and only that reference.
>
> --
> Trond Myklebust
> Linux NFS client maintainer, PrimaryData
> trond.myklebust@primarydata.com



-- 
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@primarydata.com

      reply	other threads:[~2015-02-06 13:35 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-06  4:45 [PATCH v3 1/5] NFSv4: Ensure we reference the inode for return-on-close in delegreturn Trond Myklebust
2015-02-06  4:45 ` [PATCH v3 2/5] NFSv4.1: Pin the inode and super block in asynchronous layoutcommit Trond Myklebust
2015-02-06  4:45   ` [PATCH v3 3/5] NFSv4.1: Pin the inode and super block in asynchronous layoutreturns Trond Myklebust
2015-02-06  4:45     ` [PATCH v3 4/5] NFSv4.1: pnfs_send_layoutreturn should use GFP_NOFS Trond Myklebust
2015-02-06  4:45       ` [PATCH v3 5/5] NFSv4.1: Fix pnfs_put_lseg races Trond Myklebust
2015-02-06  6:53         ` Peng Tao
2015-02-06  7:02           ` Peng Tao
2015-02-06 12:26 ` [PATCH v3 1/5] NFSv4: Ensure we reference the inode for return-on-close in delegreturn Jeff Layton
2015-02-06 13:31   ` Trond Myklebust
2015-02-06 13:35     ` Trond Myklebust [this message]

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