Re: [take12 3/3] kevent: Timer notifications.

Arjan van de Ven
2006-08-21T12:14:16Z

On Mon, 2006-08-21 at 15:59 +0400, Evgeniy Polyakov wrote:
> On Mon, Aug 21, 2006 at 01:27:22PM +0200, Arjan van de Ven (arjan@infradead.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.

ok... but since kevent doesn't know what is in it, wouldn't the locking
rules need to be such that it can deal with the "worst case" event? Eg
do you really have both no knowledge of what is inside, and specific
locking implementations for the different types of content??? That
sounds rather error prone.....
(if you had consistent locking rules lockdep would be perfectly fine
with that)

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