Use f_lock to protect f_flags

Traditionally, changes to struct file->f_flags have been done under BKL
protection, or with no protection at all.  This patch causes all f_flags
changes after file open/creation time to be done under protection of
f_lock.  This allows the removal of some BKL usage and fixes a number of
longstanding (if microscopic) races.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index 54b4077fed79..a8ddadbc7459 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -1156,10 +1156,12 @@ SYSCALL_DEFINE3(mq_getsetattr, mqd_t, mqdes,
         omqstat.mq_flags = filp->f_flags & O_NONBLOCK;
         if (u_mqstat) {
                 audit_mq_getsetattr(mqdes, &mqstat);
+                spin_lock(&filp->f_lock);
                 if (mqstat.mq_flags & O_NONBLOCK)
                         filp->f_flags |= O_NONBLOCK;
                 else
                         filp->f_flags &= ~O_NONBLOCK;
+                spin_unlock(&filp->f_lock);
 
                 inode->i_atime = inode->i_ctime = CURRENT_TIME;
         }