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, 4 insertions, 3 deletions

diff --git a/fs/ioctl.c b/fs/ioctl.c
index 240ec63984c..421aab465da 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -404,10 +404,12 @@ static int ioctl_fionbio(struct file *filp, int __user *argp)
         if (O_NONBLOCK != O_NDELAY)
                 flag |= O_NDELAY;
 #endif
+        spin_lock(&filp->f_lock);
         if (on)
                 filp->f_flags |= flag;
         else
                 filp->f_flags &= ~flag;
+        spin_unlock(&filp->f_lock);
         return error;
 }
 
@@ -432,10 +434,12 @@ static int ioctl_fioasync(unsigned int fd, struct file *filp,
         if (error)
                 return error;
 
+        spin_lock(&filp->f_lock);
         if (on)
                 filp->f_flags |= FASYNC;
         else
                 filp->f_flags &= ~FASYNC;
+        spin_unlock(&filp->f_lock);
         return error;
 }
 
@@ -499,10 +503,7 @@ int do_vfs_ioctl(struct file *filp, unsigned int fd, unsigned int cmd,
                 break;
 
         case FIONBIO:
-                /* BKL needed to avoid races tweaking f_flags */
-                lock_kernel();
                 error = ioctl_fionbio(filp, argp);
-                unlock_kernel();
                 break;
 
         case FIOASYNC: