Re: [patch, validator] fix proc_subdir_lock related deadlock

[Ingo Molnar <mingo@elte.hu>]

* Andrew Morton <akpm@osdl.org> wrote:

> > to solve this we must either change files_lock to be softirq-safe too 
> > (bleh!), or we must forbid remove_proc_entry() use from softirq 
> > contexts. Neither is a happy solution - remove_proc_entry() is used 
> > within free_irq(), and who knows how many drivers do free_irq() in 
> > softirq/tasklet context ...
> 
> free_irq()'s /proc fiddling has always been a pain - we just shouldn't 
> be doing filesystem things in irq/bh context.

the second patch i sent is quite straightforward.

> > Andrew, this needs to be resolved before v2.6.16, correct? Steve's patch 
> > solves a real bug in the upstream kernel.
> 
> It's not a very big bug - I think only Steve hit it, and that with a 
> stress-test which was somewhat tuned to hit it.

still ...

> So we can afford to sit on the problem for a while, as long as someone 
> is working on a broader /proc-sanity fix.  But nobody will do that.
> 
> I wonder if we can just punt the unregister_handler_proc/kfree up to a 
> keventd callback.

i'd rather do the files_lock change i sent, and perhaps add a 
WARN_ON_ONCE() to all known places that do a free_irq() from softirq 
context.

	Ingo