linux-kernel - [PATCH] fs/super.c: do not shrink fs slab during direct memory reclaim

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Date:	Fri, 29 Aug 2014 17:57:22 +0800
From:	Xue jiufei <xuejiufei@...wei.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<linux-fsdevel@...r.kernel.org>,
	"ocfs2-devel@....oracle.com" <ocfs2-devel@....oracle.com>,
	Junxiao Bi <junxiao.bi@...cle.com>
Subject: [PATCH] fs/super.c: do not shrink fs slab during direct memory reclaim

The patch trys to solve one deadlock problem caused by cluster
fs, like ocfs2. And the problem may happen at least in the below
situations:
1)Receiving a connect message from other nodes, node queues a
work_struct o2net_listen_work.
2)o2net_wq processes this work and calls sock_alloc() to allocate
memory for a new socket.
3)It would do direct memory reclaim when available memory is not
enough and trigger the inode cleanup. That inode being cleaned up
is happened to be ocfs2 inode, so call evict()->ocfs2_evict_inode()
->ocfs2_drop_lock()->dlmunlock()->o2net_send_message_vec(),
and wait for the unlock response from master.
4)tcp layer received the response, call o2net_data_ready() and
queue sc_rx_work, waiting o2net_wq to process this work.
5)o2net_wq is a single thread workqueue, it process the work one by
one. Right now it is still doing o2net_listen_work and cannot handle
sc_rx_work. so we deadlock.

It is impossible to set GFP_NOFS for memory allocation in sock_alloc().
So we use PF_FSTRANS to avoid the task reentering filesystem when
available memory is not enough.

Signed-off-by: joyce.xue <xuejiufei@...wei.com>
---
 fs/ocfs2/cluster/tcp.c | 7 +++++++
 fs/super.c             | 3 +++
 2 files changed, 10 insertions(+)

diff --git a/fs/ocfs2/cluster/tcp.c b/fs/ocfs2/cluster/tcp.c
index 681691b..629b4da 100644
--- a/fs/ocfs2/cluster/tcp.c
+++ b/fs/ocfs2/cluster/tcp.c
@@ -1581,6 +1581,8 @@ static void o2net_start_connect(struct work_struct *work)
 	int ret = 0, stop;
 	unsigned int timeout;
 
+	current->flags |= PF_FSTRANS;
+
 	/* if we're greater we initiate tx, otherwise we accept */
 	if (o2nm_this_node() <= o2net_num_from_nn(nn))
 		goto out;
@@ -1683,6 +1685,7 @@ out:
 	if (mynode)
 		o2nm_node_put(mynode);
 
+	current->flags &= ~PF_FSTRANS;
 	return;
 }
 
@@ -1809,6 +1812,8 @@ static int o2net_accept_one(struct socket *sock, int *more)
 	struct o2net_sock_container *sc = NULL;
 	struct o2net_node *nn;
 
+	current->flags |= PF_FSTRANS;
+
 	BUG_ON(sock == NULL);
 	*more = 0;
 	ret = sock_create_lite(sock->sk->sk_family, sock->sk->sk_type,
@@ -1918,6 +1923,8 @@ out:
 		o2nm_node_put(local_node);
 	if (sc)
 		sc_put(sc);
+
+	current->flags &= ~PF_FSTRANS;
 	return ret;
 }
 
diff --git a/fs/super.c b/fs/super.c
index b9a214d..c4a8dc1 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -71,6 +71,9 @@ static unsigned long super_cache_scan(struct shrinker *shrink,
 	if (!(sc->gfp_mask & __GFP_FS))
 		return SHRINK_STOP;
 
+	if (current->flags & PF_FSTRANS)
+		return SHRINK_STOP;
+
 	if (!grab_super_passive(sb))
 		return SHRINK_STOP;
 
-- 
1.8.4.3

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