vfs: take f_lock on modifying f_mode after open time
Wu Fengguang [Fri, 5 Mar 2010 21:42:01 +0000 (13:42 -0800)]
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>

fs/file_table.c
fs/nfsd/nfs4state.c

index b98404b..32d12b7 100644 (file)
@@ -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);
index f19ed86..fcafe60 100644 (file)
@@ -1998,7 +1998,9 @@ nfs4_file_downgrade(struct file *filp, unsigned int share_access)
 {
        if (share_access & NFS4_SHARE_ACCESS_WRITE) {
                drop_file_write_access(filp);
+               spin_lock(&filp->f_lock);
                filp->f_mode = (filp->f_mode | FMODE_READ) & ~FMODE_WRITE;
+               spin_unlock(&filp->f_lock);
        }
 }