Re: [PATCH 7/9] nfs: add code to allow client to wait on lock callbacks

[Anna Schumaker <Anna.Schumaker@netapp.com>]

Hi Jeff,

On 09/06/2016 11:12 AM, Jeff Layton wrote:
> Add a waitqueue head to the client structure. Have clients set a wait
> on that queue prior to requesting a lock from the server. If the lock
> is blocked, then we can use that to wait for wakeups.
> 
> Note that we do need to do this "manually" since we need to set the
> wait on the waitqueue prior to requesting the lock, but requesting a
> lock can involve activities that can block.
> 
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> ---
>  fs/nfs/callback_proc.c    |  1 +
>  fs/nfs/nfs4client.c       |  1 +
>  fs/nfs/nfs4proc.c         | 67 ++++++++++++++++++++++++++++++++++++++++++++---
>  include/linux/nfs_fs_sb.h |  1 +
>  4 files changed, 67 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/nfs/callback_proc.c b/fs/nfs/callback_proc.c
> index a211af339f32..4ba6a8763f91 100644
> --- a/fs/nfs/callback_proc.c
> +++ b/fs/nfs/callback_proc.c
> @@ -645,6 +645,7 @@ __be32 nfs4_callback_notify_lock(struct cb_notify_lock_args *args, void *dummy,
>  	fc_tbl = &cps->clp->cl_session->fc_slot_table;
>  
>  	status = htonl(NFS4_OK);
> +	__wake_up(&cps->clp->cl_lock_waitq, TASK_NORMAL, 0, &args->cbnl_owner);
>  	return status;
>  }
>  #endif /* CONFIG_NFS_V4_1 */
> diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c
> index cd3b7cfdde16..89b7a794ff10 100644
> --- a/fs/nfs/nfs4client.c
> +++ b/fs/nfs/nfs4client.c
> @@ -199,6 +199,7 @@ struct nfs_client *nfs4_alloc_client(const struct nfs_client_initdata *cl_init)
>  	clp->cl_minorversion = cl_init->minorversion;
>  	clp->cl_mvops = nfs_v4_minor_ops[cl_init->minorversion];
>  	clp->cl_mig_gen = 1;
> +	init_waitqueue_head(&clp->cl_lock_waitq);
>  	return clp;
>  
>  error:
> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
> index 5573f19539a6..3a6669063c44 100644
> --- a/fs/nfs/nfs4proc.c
> +++ b/fs/nfs/nfs4proc.c
> @@ -5531,13 +5531,54 @@ int nfs4_proc_delegreturn(struct inode *inode, struct rpc_cred *cred, const nfs4
>  #define NFS4_LOCK_MINTIMEOUT (1 * HZ)
>  #define NFS4_LOCK_MAXTIMEOUT (30 * HZ)
>  
> +struct nfs4_lock_waiter {
> +	struct task_struct	*task;
> +	struct nfs_lowner	*owner;
> +	bool			notified;
> +};
> +
> +static int
> +nfs4_wake_lock_waiter(wait_queue_t *wait, unsigned int mode, int flags, void *key)
> +{
> +	int ret;
> +	struct nfs4_lock_waiter	*waiter	= wait->private;
> +	struct nfs_lowner	*lowner = key, *wowner = waiter->owner;
> +
> +	/* Don't wake anybody if the string looked bogus */
> +	if (!lowner->id && !lowner->s_dev)
> +		return 0;
> +
> +	/* Only wake if the callback was for the same owner */
> +	if (lowner->clientid != wowner->clientid ||
> +	    lowner->id != wowner->id		 ||
> +	    lowner->s_dev != wowner->s_dev)
> +		return 0;
> +
> +	waiter->notified = true;
> +
> +	/* override "private" so we can use default_wake_function */
> +	wait->private = waiter->task;
> +	ret = autoremove_wake_function(wait, mode, flags, key);
> +	wait->private = waiter;
> +	return ret;
> +}
> +
>  /* 
>   * sleep, with exponential backoff, and retry the LOCK operation. 
>   */
>  static unsigned long
> -nfs4_set_lock_task_retry(unsigned long timeout)
> +nfs4_wait_for_lock_retry(unsigned long timeout, wait_queue_head_t *q,
> +			 struct nfs4_lock_waiter *waiter)
>  {
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&q->lock, flags);
> +	if (waiter->notified) {
> +		spin_unlock_irqrestore(&q->lock, flags);
> +		return timeout;
> +	}
>  	set_current_state(TASK_INTERRUPTIBLE);
> +	spin_unlock_irqrestore(&q->lock, flags);
>  	freezable_schedule_timeout_unsafe(timeout);
>  	timeout <<= 1;
>  	if (timeout > NFS4_LOCK_MAXTIMEOUT)
> @@ -6232,10 +6273,30 @@ nfs4_proc_lock(struct file *filp, int cmd, struct file_lock *request)
>  		return status;
>  
>  	do {
> +		struct nfs4_lock_state *lsp = request->fl_u.nfs4_fl.owner;
> +		struct nfs_server *server = NFS_SERVER(lsp->ls_state->inode);
> +		struct nfs_client *clp = server->nfs_client;
> +		struct nfs_lowner owner = { .clientid = clp->cl_clientid,
> +					    .id = lsp->ls_seqid.owner_id,
> +					    .s_dev = server->s_dev };
> +		struct nfs4_lock_waiter waiter = { .task  = current,
> +						   .owner = &owner,
> +						   .notified = false };
> +		wait_queue_t wait;
> +
> +		init_wait(&wait);
> +		wait.private = &waiter;
> +		wait.func = nfs4_wake_lock_waiter;
> +
> +		add_wait_queue(&clp->cl_lock_waitq, &wait);
>  		status = nfs4_proc_setlk(state, cmd, request);
> -		if ((status != -EAGAIN) || IS_SETLK(cmd))
> +		if ((status != -EAGAIN) || IS_SETLK(cmd)) {
> +			finish_wait(&clp->cl_lock_waitq, &wait);
>  			break;
> -		timeout = nfs4_set_lock_task_retry(timeout);
> +		}
> +		timeout = nfs4_wait_for_lock_retry(timeout,
> +					&clp->cl_lock_waitq, &waiter);
> +		finish_wait(&clp->cl_lock_waitq, &wait);

I'm curious why you didn't turn everything in this do-while loop into a new function?  This code might be cleaner that way :)

Thanks,
Anna

>  		status = -ERESTARTSYS;
>  		if (signalled())
>  			break;
> diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
> index 14a762d2734d..fb2319a0ce65 100644
> --- a/include/linux/nfs_fs_sb.h
> +++ b/include/linux/nfs_fs_sb.h
> @@ -103,6 +103,7 @@ struct nfs_client {
>  #define NFS_SP4_MACH_CRED_WRITE    5	/* WRITE */
>  #define NFS_SP4_MACH_CRED_COMMIT   6	/* COMMIT */
>  #define NFS_SP4_MACH_CRED_PNFS_CLEANUP  7 /* LAYOUTRETURN */
> +	wait_queue_head_t	cl_lock_waitq;
>  #endif /* CONFIG_NFS_V4 */
>  
>  	/* Our own IP address, as a null-terminated string.
>