[PATCH] nfs: don't hold rcu_read_lock over xs_swapper call

[Jeff Layton]

Jerome reported seeing a WARN_ON pop up when enabling a swapfile on NFS.
The xs_swapper call can sleep so we do not want to hold the
rcu_read_lock when calling it. Fix this by taking a reference to the
xprt in the critical section, calling xs_swapper outside it and then
putting that reference.

Reported-by: Jerome Marchand <jmarchan@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Signed-off-by: Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx>
---
 fs/nfs/file.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 8b8d83a526ce..3ee08460c4cf 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -561,12 +561,18 @@ static int nfs_swap_activate(struct swap_info_struct *sis, struct file *file,
 {
 	int ret;
 	struct rpc_clnt *clnt = NFS_CLIENT(file->f_mapping->host);
+	struct rpc_xprt *xprt;
 
 	*span = sis->pages;
 
 	rcu_read_lock();
-	ret = xs_swapper(rcu_dereference(clnt->cl_xprt), 1);
+	xprt = xprt_get(rcu_dereference(clnt->cl_xprt));
 	rcu_read_unlock();
+	if (!xprt)
+		return -EINVAL;
+
+	ret = xs_swapper(xprt, 1);
+	xprt_put(xprt);
 
 	return ret;
 }
@@ -574,10 +580,16 @@ static int nfs_swap_activate(struct swap_info_struct *sis, struct file *file,
 static void nfs_swap_deactivate(struct file *file)
 {
 	struct rpc_clnt *clnt = NFS_CLIENT(file->f_mapping->host);
+	struct rpc_xprt *xprt;
 
 	rcu_read_lock();
-	xs_swapper(rcu_dereference(clnt->cl_xprt), 0);
+	xprt = xprt_get(rcu_dereference(clnt->cl_xprt));
 	rcu_read_unlock();
+	if (!xprt)
+		return;
+
+	xs_swapper(xprt, 0);
+	xprt_put(xprt);
 }
 #endif
 
-- 
2.4.1


--MP_/VPZ066Oa6ok3CTMlO2eJBgV--
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