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, 3 deletions

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index bc84e125c6bc..224f271d8cbe 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -2162,13 +2162,12 @@ static int fionbio(struct file *file, int __user *p)
         if (get_user(nonblock, p))
                 return -EFAULT;
 
-        /* file->f_flags is still BKL protected in the fs layer - vomit */
-        lock_kernel();
+        spin_lock(&file->f_lock);
         if (nonblock)
                 file->f_flags |= O_NONBLOCK;
         else
                 file->f_flags &= ~O_NONBLOCK;
-        unlock_kernel();
+        spin_unlock(&file->f_lock);
         return 0;
 }