vfs: take f_lock on modifying f_mode after open time

We'll introduce FMODE_RANDOM which will be runtime modified.  So protect
all runtime modification to f_mode with f_lock to avoid races.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: <stable@kernel.org>			[2.6.33.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/file_table.c b/fs/file_table.c
index b98404b54383..32d12b78bac8 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -393,7 +393,9 @@ retry:
                         continue;
                 if (!(f->f_mode & FMODE_WRITE))
                         continue;
+                spin_lock(&f->f_lock);
                 f->f_mode &= ~FMODE_WRITE;
+                spin_unlock(&f->f_lock);
                 if (file_check_writeable(f) != 0)
                         continue;
                 file_release_write(f);