NFS: Fix nfs_file_llseek()

After the BKL removal patches were applied to the rest of the NFS code, the
BKL protection in nfs_file_llseek() is no longer sufficient to ensure that
inode->i_size is read safely in generic_file_llseek_unlocked().

In order to fix the situation, we either have to replace the naked read of
inode->i_size in generic_file_llseek_unlocked() with i_size_read(), or the
whole thing needs to be executed under the inode->i_lock;
In order to avoid disrupting other filesystems, avoid touching
generic_file_llseek_unlocked() for now...

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 78460657f5cb..3ddb00433f4f 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -188,13 +188,16 @@ static loff_t nfs_file_llseek(struct file *filp, loff_t offset, int origin)
         /* origin == SEEK_END => we must revalidate the cached file length */
         if (origin == SEEK_END) {
                 struct inode *inode = filp->f_mapping->host;
+
                 int retval = nfs_revalidate_file_size(inode, filp);
                 if (retval < 0)
                         return (loff_t)retval;
-        }
-        lock_kernel();  /* BKL needed? */
-        loff = generic_file_llseek_unlocked(filp, offset, origin);
-        unlock_kernel();
+
+                spin_lock(&inode->i_lock);
+                loff = generic_file_llseek_unlocked(filp, offset, origin);
+                spin_unlock(&inode->i_lock);
+        } else
+                loff = generic_file_llseek_unlocked(filp, offset, origin);
         return loff;
 }