linux-kernel - Re: [take12 3/3] kevent: Timer notifications.

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Message-ID: <20060821115947.GE8608@2ka.mipt.ru>
Date:	Mon, 21 Aug 2006 15:59:47 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Christoph Hellwig <hch@...radead.org>,
	lkml <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Ulrich Drepper <drepper@...hat.com>,
	Andrew Morton <akpm@...l.org>, netdev <netdev@...r.kernel.org>,
	Zach Brown <zach.brown@...cle.com>, tglx@...utronix.de
Subject: Re: [take12 3/3] kevent: Timer notifications.

On Mon, Aug 21, 2006 at 01:27:22PM +0200, Arjan van de Ven (arjan@...radead.org) wrote:
> On Mon, 2006-08-21 at 15:18 +0400, Evgeniy Polyakov wrote:
> > ]> > +	lockdep_set_class(&t->ktimer_storage.lock, &kevent_timer_key);
> > > 
> > > When looking at the kevent_storage_init callers most need to do
> > > those lockdep_set_class class.  Shouldn't kevent_storage_init just
> > > get a "struct lock_class_key *" argument?
> > 
> > It will not work, since inode is used for both socket and inode
> > notifications (to save some space in struct sock), lockdep initalization
> > is performed on the highest level, so I put it alone.
> 
> Call me a cynic, but I'm always a bit sceptical about needing lockdep
> annotations like this... Can you explain why you need it in this case,
> including the proof that it's safe?

Ok, again :)
Kevent uses meaning of storage of kevents without any special knowledge
what is is (inode, socket, file, timer - anything), so it's
initalization function among other things calls spin_lock_init().
Lockdep inserts static variable just before real spinlock
initialization, and since all locks are initialized in the same place,
all of them get the same static magic.
Later those locks are used in different context (for example inode
notificatins only in process context, but socket can be called from BH
context), since lockdep thinks they are the same, it screams.
Obviously the same inode can not be used for sockets and files, so I
added above lockdep initialization.

-- 
	Evgeniy Polyakov
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