linux-kernel - Re: Crashes in next-20160915 (BUG at fs/notify/notification.c:66!)

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Message-ID: <20160921091511.GC3725@quack2.suse.cz>
Date:   Wed, 21 Sep 2016 11:15:11 +0200
From:   Jan Kara <jack@...e.cz>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>,
        Guenter Roeck <linux@...ck-us.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Crashes in next-20160915 (BUG at fs/notify/notification.c:66!)

On Tue 20-09-16 22:05:00, Michael Ellerman wrote:
> Andrew Morton <akpm@...ux-foundation.org> writes:
> > On Tue, 20 Sep 2016 11:10:35 +1000 Michael Ellerman <mpe@...erman.id.au> wrote:
> >> Jan Kara <jack@...e.cz> writes:
> >> >
> >> > Right, that was the problem. spin_is_locked() without CONFIG_SPINLOCK_DEBUG
> >> > returns always 0.
> >> 
> >> Can we get this fixed soon please? It's breaking all my CI runs.
> >
> > It should be fixed in next -next.
> 
> Great thanks.
> 
> I did search LKML to see if Jan had sent a fix but I guess I missed it.

I didn't send the fix to LKML but only to linux-fsdevel...

> > diff -puN fs/notify/fanotify/fanotify_user.c~fsnotify-convert-notification_mutex-to-a-spinlock-fix fs/notify/fanotify/fanotify_user.c
> > --- a/fs/notify/fanotify/fanotify_user.c~fsnotify-convert-notification_mutex-to-a-spinlock-fix
> > +++ a/fs/notify/fanotify/fanotify_user.c
> > @@ -54,7 +54,8 @@ struct kmem_cache *fanotify_perm_event_c
> >  static struct fsnotify_event *get_one_event(struct fsnotify_group *group,
> >  					    size_t count)
> >  {
> > -	BUG_ON(!spin_is_locked(&group->notification_lock));
> > +	BUG_ON(IS_ENABLED(CONFIG_SMP) &&
> > +	       !spin_is_locked(&group->notification_lock));
>   
> I thought lockdep_assert_held() was preferred for checks like this that
> are purely sanity checking, ie. not part of the algorithm.

As pointed out by other guy, assert_spin_locked() is probably the right way
to do it (it's a wrapper that does essentially what I did here). Somehow I
missed that when looking for the right fix.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR