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 <[email protected]> Reported-by: Larry Finger <[email protected]> Reported-by: Wu Fengguang <[email protected]> Signed-off-by: Jonathan Corbet <[email protected]>
kev009 · Mar 30, 2009 · 4a6a449 · 4a6a449
1 parent 996ff68
commit 4a6a449
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Showing 2 changed files with 8 additions and 4 deletions.
diff --git 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;
 }
 

diff --git a/include/linux/fs.h b/include/linux/fs.h
@@ -848,7 +848,7 @@ struct file {
 #define f_dentry	f_path.dentry
 #define f_vfsmnt	f_path.mnt
 	const struct file_operations	*f_op;
-	spinlock_t		f_lock;  /* f_ep_links, f_flags */
+	spinlock_t		f_lock;  /* f_ep_links, f_flags, no IRQ */
 	atomic_long_t		f_count;
 	unsigned int 		f_flags;
 	fmode_t			f_mode;