[PATCH 3.12 18/40] NFS: Fix races in nfs_revalidate_mapping

[Jiri Slaby]

From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 17dfeb9113397a6119091a491ef7182649f0c5a9 upstream.

Commit d529ef83c355f97027ff85298a9709fe06216a66 (NFS: fix the handling
of NFS_INO_INVALID_DATA flag in nfs_revalidate_mapping) introduces
a potential race, since it doesn't test the value of nfsi->cache_validity
and set the bitlock in nfsi->flags atomically.

Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Cc: Jeff Layton <jlayton@xxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 fs/nfs/inode.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 9b6c90a8a311..12c0fa8ae004 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -1048,24 +1048,24 @@ int nfs_revalidate_mapping(struct inode *inode, struct address_space *mapping)
 				  nfs_wait_bit_killable, TASK_KILLABLE);
 		if (ret)
 			goto out;
-		if (!(nfsi->cache_validity & NFS_INO_INVALID_DATA))
-			goto out;
-		if (!test_and_set_bit_lock(NFS_INO_INVALIDATING, bitlock))
+		spin_lock(&inode->i_lock);
+		if (test_bit(NFS_INO_INVALIDATING, bitlock)) {
+			spin_unlock(&inode->i_lock);
+			continue;
+		}
+		if (nfsi->cache_validity & NFS_INO_INVALID_DATA)
 			break;
-	}
-
-	spin_lock(&inode->i_lock);
-	if (nfsi->cache_validity & NFS_INO_INVALID_DATA) {
-		nfsi->cache_validity &= ~NFS_INO_INVALID_DATA;
-		spin_unlock(&inode->i_lock);
-		trace_nfs_invalidate_mapping_enter(inode);
-		ret = nfs_invalidate_mapping(inode, mapping);
-		trace_nfs_invalidate_mapping_exit(inode, ret);
-	} else {
-		/* something raced in and cleared the flag */
 		spin_unlock(&inode->i_lock);
+		goto out;
 	}
 
+	set_bit(NFS_INO_INVALIDATING, bitlock);
+	nfsi->cache_validity &= ~NFS_INO_INVALID_DATA;
+	spin_unlock(&inode->i_lock);
+	trace_nfs_invalidate_mapping_enter(inode);
+	ret = nfs_invalidate_mapping(inode, mapping);
+	trace_nfs_invalidate_mapping_exit(inode, ret);
+
 	clear_bit_unlock(NFS_INO_INVALIDATING, bitlock);
 	smp_mb__after_clear_bit();
 	wake_up_bit(bitlock, NFS_INO_INVALIDATING);
-- 
1.9.1

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