Re: [PATCH RFC 1/4] Generic BUG handling.

From: Andrew Morton
Date: Thu Sep 28 2006 - 20:08:23 EST

On Thu, 28 Sep 2006 16:43:55 -0700
Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:

> Andrew Morton wrote:
> > What is the locking for these lists? I don't see much in here. It has
> > implications for code which wants to do BUG while holding that lock..
> >
> There's no locking. This is a direct copy of the original powerpc
> code. I assume, but haven't checked, that there's a lock to serialize
> module loading/unloading, so the insertion/deletion is all properly
> synchronized.
> The only other user is traversal when actually handling a bug; if you're
> very unlucky this could happen while you're actually loading/unloading
> and you would see the list in an inconsistent state. I guess we could
> put a lock there, and trylock it on traversal; at least that would stop
> a concurrent modload/unload from getting in there while we're trying to
> walk the list.

The module_bug_cleanup() code is in a stop_machine_run() callback, so
that's all OK.

I _think_ your module_bug_finalize()'s list_add() could race with another
CPU's BUG_ON(). We can live with that.

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