Messages in this thread | | | Subject | Re: [PATCH -v3 5/8] fsnotify: unified filesystem notification backend | From | Peter Zijlstra <> | Date | Sat, 29 Nov 2008 00:39:29 +0100 |
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On Fri, 2008-11-28 at 18:22 -0500, Eric Paris wrote: > On Thu, 2008-11-27 at 17:20 +0100, Peter Zijlstra wrote: > > On Tue, 2008-11-25 at 12:21 -0500, Eric Paris wrote: > > > +int fsnotify_check_notif_queue(struct fsnotify_group *group) > > > +{ > > > + mutex_lock(&group->notification_mutex); > > > + if (!list_empty(&group->notification_list)) > > > + return 1; > > > + mutex_unlock(&group->notification_mutex); > > > + return 0; > > > +} > > > > > +void fsnotify_clear_notif(struct fsnotify_group *group) > > > +{ > > > + struct fsnotify_event *event; > > > + > > > + while (fsnotify_check_notif_queue(group)) { > > > + event = get_event_from_notif(group); > > > + fsnotify_put_event(event); > > > + /* fsnotify_check_notif_queue() took this lock */ > > > + mutex_unlock(&group->notification_mutex); > > > + } > > > +} > > > > That is quite horrible, please just open code that to keep the locking > > symmetric. > > While horrible, I use fsnotify_check_notif_queue in my fsnotify (not in > this series as this only includes dnotify) has > > wait_event_interruptible(group->notification_waitq, fanotify_check_notif_queue(group)); > > So I wouldn't know how to open code that... I can open code this > instance, but it's going to mean redoing all of that other code to > handle having thing not be present when we return. Since I didn't > submit that as well I guess I'm not allowed to use it as a reason...
Or you add a lock parameter to wait_event*() which gets unlocked before schedule and locks again afterwards.
That would allow you to write it like so:
mutex_lock(&group->notification_mutex); wait_event_interruptible_lock(group->notification_waitq, !list_empty(&group_notificatioin_list), &group_notification_mutex);
/* handle the !empty list */ mutex_unlock(&group->notification_mutex);
You could use the type matching magic we have to select between spinlock/mutex operations for the lock argument.
I've come across such a pattern a few times, most of the times we end up open coding the wait_event stuff.
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