Messages in this thread | | | Date | Wed, 10 Sep 2014 18:58:48 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] perf, x86: Fall back to vmalloc for BTS buffer allocation |
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On Wed, Sep 10, 2014 at 06:35:56PM +0200, Peter Zijlstra wrote: > On Wed, Sep 10, 2014 at 04:40:12PM +0200, Andi Kleen wrote: > > > We did this once, and that blew up big time. > > > > > > Even now, vmalloc_fault() has a very explicit: > > > > > > WARN_ON_ONCE(in_nmi()); > > > > > > So this isn't going to happen until you fix that. > > > > Good point. > > > > We just need to call vmalloc_sync_all at allocation time, > > no need to change vmalloc_fault. > > Somehow that wasn't considered adequate, but lemme try and dig out that > thread. It should be somewhere... > > https://lkml.org/lkml/2010/7/14/465
Note that since then we have actually fixed the 'cannot fault from NMI context' thing, so we should be able to actually take those faults. I suspect we can simply remove those WARNs from the vmalloc fault path, but it would need double checking to see if there's no other reasons.
Also:
https://lkml.org/lkml/2014/4/10/581 https://patchwork.kernel.org/patch/3048111/
I'm not entirely sure what the final conclusion is, except to note that it didn't happen.
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