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Commit 3c87ef6e authored by Jeff Layton's avatar Jeff Layton Committed by Trond Myklebust
Browse files

sunrpc: keep a count of swapfiles associated with the rpc_clnt 



Jerome reported seeing a warning pop when working with a swapfile on
NFS. The nfs_swap_activate can end up calling sk_set_memalloc while
holding the rcu_read_lock and that function can sleep.

To fix that, we need to take a reference to the xprt while holding the
rcu_read_lock, set the socket up for swapping and then drop that
reference. But, xprt_put is not exported and having NFS deal with the
underlying xprt is a bit of layering violation anyway.

Fix this by adding a set of activate/deactivate functions that take a
rpc_clnt pointer instead of an rpc_xprt, and have nfs_swap_activate and
nfs_swap_deactivate call those.

Also, add a per-rpc_clnt atomic counter to keep track of the number of
active swapfiles associated with it. When the counter does a 0->1
transition, we enable swapping on the xprt, when we do a 1->0 transition
we disable swapping on it.

This also allows us to be a bit more selective with the RPC_TASK_SWAPPER
flag. If non-swapper and swapper clnts are sharing a xprt, then we only
need to flag the tasks from the swapper clnt with that flag.

Acked-by: default avatarMel Gorman <mgorman@suse.de>
Reported-by: default avatarJerome Marchand <jmarchan@redhat.com>
Signed-off-by: default avatarJeff Layton <jeff.layton@primarydata.com>
Reviewed-by: default avatarChuck Lever <chuck.lever@oracle.com>
Signed-off-by: default avatarTrond Myklebust <trond.myklebust@primarydata.com>
parent 0d2a970d

fs/nfs/file.c

+2 −13
Original line number Diff line number Diff line
@@ -555,31 +555,22 @@ static int nfs_launder_page(struct page *page) 
	return nfs_wb_page(inode, page);

}



#ifdef CONFIG_NFS_SWAP

static int nfs_swap_activate(struct swap_info_struct *sis, struct file *file,

						sector_t *span)

{

	int ret;

	struct rpc_clnt *clnt = NFS_CLIENT(file->f_mapping->host);



	*span = sis->pages;



	rcu_read_lock();

	ret = xs_swapper(rcu_dereference(clnt->cl_xprt), 1);

	rcu_read_unlock();



	return ret;

	return rpc_clnt_swap_activate(clnt);

}



static void nfs_swap_deactivate(struct file *file)

{

	struct rpc_clnt *clnt = NFS_CLIENT(file->f_mapping->host);



	rcu_read_lock();

	xs_swapper(rcu_dereference(clnt->cl_xprt), 0);

	rcu_read_unlock();

	rpc_clnt_swap_deactivate(clnt);

}

#endif



const struct address_space_operations nfs_file_aops = {

	.readpage = nfs_readpage,
@@ -596,10 +587,8 @@ const struct address_space_operations nfs_file_aops = { 
	.launder_page = nfs_launder_page,

	.is_dirty_writeback = nfs_check_dirty_writeback,

	.error_remove_page = generic_error_remove_page,

#ifdef CONFIG_NFS_SWAP

	.swap_activate = nfs_swap_activate,

	.swap_deactivate = nfs_swap_deactivate,

#endif

};



/*

include/linux/sunrpc/clnt.h

+1 −0
Original line number Diff line number Diff line
@@ -56,6 +56,7 @@ struct rpc_clnt { 
	struct rpc_rtt *	cl_rtt;		/* RTO estimator data */

	const struct rpc_timeout *cl_timeout;	/* Timeout strategy */



	atomic_t		cl_swapper;	/* swapfile count */

	int			cl_nodelen;	/* nodename length */

	char 			cl_nodename[UNX_MAXNODENAME+1];

	struct rpc_pipe_dir_head cl_pipedir_objects;

include/linux/sunrpc/sched.h

+16 −0
Original line number Diff line number Diff line
@@ -268,4 +268,20 @@ static inline void rpc_assign_waitqueue_name(struct rpc_wait_queue *q, 
}

#endif



#if IS_ENABLED(CONFIG_SUNRPC_SWAP)

int rpc_clnt_swap_activate(struct rpc_clnt *clnt);

void rpc_clnt_swap_deactivate(struct rpc_clnt *clnt);

#else

static inline int

rpc_clnt_swap_activate(struct rpc_clnt *clnt)

{

	return -EINVAL;

}



static inline void

rpc_clnt_swap_deactivate(struct rpc_clnt *clnt)

{

}

#endif /* CONFIG_SUNRPC_SWAP */



#endif /* _LINUX_SUNRPC_SCHED_H_ */

net/sunrpc/clnt.c

+58 −9
Original line number Diff line number Diff line
@@ -891,15 +891,8 @@ void rpc_task_set_client(struct rpc_task *task, struct rpc_clnt *clnt) 
			task->tk_flags |= RPC_TASK_SOFT;

		if (clnt->cl_noretranstimeo)

			task->tk_flags |= RPC_TASK_NO_RETRANS_TIMEOUT;

		if (sk_memalloc_socks()) {

			struct rpc_xprt *xprt;



			rcu_read_lock();

			xprt = rcu_dereference(clnt->cl_xprt);

			if (xprt->swapper)

		if (atomic_read(&clnt->cl_swapper))

			task->tk_flags |= RPC_TASK_SWAPPER;

			rcu_read_unlock();

		}

		/* Add to the client's list of all tasks */

		spin_lock(&clnt->cl_lock);

		list_add_tail(&task->tk_task, &clnt->cl_tasks);
@@ -2479,3 +2472,59 @@ void rpc_show_tasks(struct net *net) 
	spin_unlock(&sn->rpc_client_lock);

}

#endif



#if IS_ENABLED(CONFIG_SUNRPC_SWAP)

int

rpc_clnt_swap_activate(struct rpc_clnt *clnt)

{

	int ret = 0;

	struct rpc_xprt	*xprt;



	if (atomic_inc_return(&clnt->cl_swapper) == 1) {

retry:

		rcu_read_lock();

		xprt = xprt_get(rcu_dereference(clnt->cl_xprt));

		rcu_read_unlock();

		if (!xprt) {

			/*

			 * If we didn't get a reference, then we likely are

			 * racing with a migration event. Wait for a grace

			 * period and try again.

			 */

			synchronize_rcu();

			goto retry;

		}



		ret = xs_swapper(xprt, 1);

		xprt_put(xprt);

	}

	return ret;

}

EXPORT_SYMBOL_GPL(rpc_clnt_swap_activate);



void

rpc_clnt_swap_deactivate(struct rpc_clnt *clnt)

{

	struct rpc_xprt	*xprt;



	if (atomic_dec_if_positive(&clnt->cl_swapper) == 0) {

retry:

		rcu_read_lock();

		xprt = xprt_get(rcu_dereference(clnt->cl_xprt));

		rcu_read_unlock();

		if (!xprt) {

			/*

			 * If we didn't get a reference, then we likely are

			 * racing with a migration event. Wait for a grace

			 * period and try again.

			 */

			synchronize_rcu();

			goto retry;

		}



		xs_swapper(xprt, 0);

		xprt_put(xprt);

	}

}

EXPORT_SYMBOL_GPL(rpc_clnt_swap_deactivate);

#endif /* CONFIG_SUNRPC_SWAP */

net/sunrpc/xprtsock.c

+1 −2
Original line number Diff line number Diff line
@@ -1955,7 +1955,7 @@ static void xs_local_connect(struct rpc_xprt *xprt, struct rpc_task *task) 
		msleep_interruptible(15000);

}



#ifdef CONFIG_SUNRPC_SWAP

#if IS_ENABLED(CONFIG_SUNRPC_SWAP)

static void xs_set_memalloc(struct rpc_xprt *xprt)

{

	struct sock_xprt *transport = container_of(xprt, struct sock_xprt,
@@ -1987,7 +1987,6 @@ int xs_swapper(struct rpc_xprt *xprt, int enable) 


	return err;

}

EXPORT_SYMBOL_GPL(xs_swapper);

#else

static void xs_set_memalloc(struct rpc_xprt *xprt)

{