Fix a lockdep warning in fasync_helper()

Lockdep gripes if file->f_lock is taken in a no-IRQ situation, since that
is not always the case.  We don't really want to disable IRQs for every
acquisition of f_lock; instead, just move it outside of fasync_lock.

Reported-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Reported-by: Larry Finger <Larry.Finger@lwfinger.net>
Reported-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 7 insertions, 3 deletions

diff --git a/fs/fcntl.c b/fs/fcntl.c
index d865ca66..cc8e4de 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -531,6 +531,12 @@ int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fap
 		if (!new)
 			return -ENOMEM;
 	}
+
+	/*
+	 * We need to take f_lock first since it's not an IRQ-safe
+	 * lock.
+	 */
+	spin_lock(&filp->f_lock);
 	write_lock_irq(&fasync_lock);
 	for (fp = fapp; (fa = *fp) != NULL; fp = &fa->fa_next) {
 		if (fa->fa_file == filp) {
@@ -555,14 +561,12 @@ int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fap
 		result = 1;
 	}
 out:
-	/* Fix up FASYNC bit while still holding fasync_lock */
-	spin_lock(&filp->f_lock);
 	if (on)
 		filp->f_flags |= FASYNC;
 	else
 		filp->f_flags &= ~FASYNC;
-	spin_unlock(&filp->f_lock);
 	write_unlock_irq(&fasync_lock);
+	spin_unlock(&filp->f_lock);
 	return result;
 }