Messages in this thread | | | Subject | Re: irq-disabled vs vmap vs text_poke | From | Peter Zijlstra <> | Date | Fri, 13 Feb 2009 14:02:18 +0100 |
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On Fri, 2009-02-13 at 13:55 +0100, Nick Piggin wrote: > On Fri, Feb 13, 2009 at 01:50:07PM +0100, Peter Zijlstra wrote: > > Hi, > > > > Ingo got the following splat:
<snip splat>
> > Which points to vunmap() being called with interrupts disabled. > > > > Which made me look at the vmap/vunmap calls, and they appear to not be > > irq-safe, therefore this would be a bug in text_poke(). > > > > [ that is, vmap() can end up calling get_vm_area_caller() which in turn > > calls __get_vm_area_node() with GFP_KERNEL, ergo, don't do this from > > an atomic context. ] > > > > Now text_poke() uses local_irq_save/restore(), which conveys that it can > > be called with IRQs disabled, which is exactly what happens in the trace > > above, however we just established that vmap/vunmap() are not irq-safe. > > > > Anybody got an idea on how to fix this? > > Oh, I thought the consensus was not to use vmap for this?
Seems like a sensible consensus, still that means text_poke() needs some TLC.
> With a bit of work, we can make vunmap irq-safe with the lazy vunmapping > infrastructure (vmap could also be irq-safe, but would be subject to > spurious failures due to being unable to flush lazy vunmaps.
*nod*
> I think I got a mostly working patch cobbled together sitting here > somewhere. I was waiting for some _really_ good use case before spending > more time on it. I would prefer if at all possible to do vmap operations > in sleepable, process context.
Agreed, I think we want to fix text_poke() and make the vmap/vunmap() ops yell louder at violations of these rules.
I'm just totally clueless wrt text_poke() hence this email ;-)
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