From 6f23e3872cff238589f9bf39c71db2ea880c9a26 Mon Sep 17 00:00:00 2001
From: Trond Myklebust <Trond.Myklebust@netapp.com>
Date: Fri, 25 Jan 2008 16:38:17 -0500
Subject: NFS: Fix a potential race between umount and
 nfs_access_cache_shrinker()

Thanks to Yawei Niu for spotting the race.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
---
 fs/nfs/dir.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

(limited to 'fs/nfs/dir.c')

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 5ca762de88bf..476cb0f837fd 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1694,13 +1694,19 @@ int nfs_access_cache_shrinker(int nr_to_scan, gfp_t gfp_mask)
 restart:
 	spin_lock(&nfs_access_lru_lock);
 	list_for_each_entry(nfsi, &nfs_access_lru_list, access_cache_inode_lru) {
+		struct rw_semaphore *s_umount;
 		struct inode *inode;
 
 		if (nr_to_scan-- == 0)
 			break;
+		s_umount = &nfsi->vfs_inode.i_sb->s_umount;
+		if (!down_read_trylock(s_umount))
+			continue;
 		inode = igrab(&nfsi->vfs_inode);
-		if (inode == NULL)
+		if (inode == NULL) {
+			up_read(s_umount);
 			continue;
+		}
 		spin_lock(&inode->i_lock);
 		if (list_empty(&nfsi->access_cache_entry_lru))
 			goto remove_lru_entry;
@@ -1719,6 +1725,7 @@ remove_lru_entry:
 		spin_unlock(&inode->i_lock);
 		spin_unlock(&nfs_access_lru_lock);
 		iput(inode);
+		up_read(s_umount);
 		goto restart;
 	}
 	spin_unlock(&nfs_access_lru_lock);
-- 
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