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Commit 4a6a4499 authored by Jonathan Corbet's avatar Jonathan Corbet
Browse files

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: default avatarBartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Reported-by: default avatarLarry Finger <Larry.Finger@lwfinger.net>
Reported-by: default avatarWu Fengguang <fengguang.wu@intel.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 996ff68d

fs/fcntl.c

+7 −3
Original line number Diff line number Diff line
@@ -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;

}

include/linux/fs.h

+1 −1
Original line number Diff line number Diff line
@@ -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;