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/sound/oss/au1550_ac97.c b/sound/oss/au1550_ac97.c
index 81e1f443d094..4191acccbcdb 100644
--- a/sound/oss/au1550_ac97.c
+++ b/sound/oss/au1550_ac97.c
@@ -1627,7 +1627,9 @@ au1550_ioctl(struct inode *inode, struct file *file, unsigned int cmd,
                                     sizeof(abinfo)) ? -EFAULT : 0;
 
         case SNDCTL_DSP_NONBLOCK:
+                spin_lock(&file->f_lock);
                 file->f_flags |= O_NONBLOCK;
+                spin_unlock(&file->f_lock);
                 return 0;
 
         case SNDCTL_DSP_GETODELAY: