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>

2 files changed, 8 insertions, 4 deletions

diff --git a/fs/fcntl.c b/fs/fcntl.c
index d865ca66ccba..cc8e4de2fee5 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;
 }
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 7428c6d35e65..2f13c1d77812 100644
--- 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;