Messages in this thread | | | Date | Tue, 15 Oct 2013 10:19:47 -0400 | From | Steven Rostedt <> | Subject | Re: Panic and page fault in loop during handling NMI backtrace handler |
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On Tue, 15 Oct 2013 14:54:11 +0200 Frederic Weisbecker <fweisbec@gmail.com> wrote:
> On Tue, Oct 15, 2013 at 02:37:17PM +0200, Peter Zijlstra wrote: > > On Tue, Oct 15, 2013 at 02:18:53PM +0200, Frederic Weisbecker wrote: > > > On Tue, Oct 15, 2013 at 02:01:04AM +0000, Liu, Chuansheng wrote: > > > > We meet one issue that during trigger all CPU backtrace, but during in the NMI handler arch_trigger_all_cpu_backtrace_handler, > > > > It hit the PAGE fault, then PAGE fault is in loop, at last the thread stack overflow, and system panic. > > > > > > > > Anyone can give some help? Thanks. > > > > > > Looks like we re-enter the fault several times. On x86-32, NMIs can > > > fault if they dereference vmalloc'ed area. I wonder if the module thing > > > we lookup in the NMI is stored on some vmalloc'ed area. > > > > IIRC modules are indeed allocated using vmalloc. See module_alloc() > > using vmalloc_exec() > > Right. At least the module text. Now I'm not sure the module_address_lookup() > dereference that. But there many other objects allocated in module.c that use > alloc_percpu(), which in turn can use vmalloc. > > IIRC Steve made the NMIs safely faultable. So may be we can remove the WARN_ON in > do_page_fault(). It may not be a good idea to allow fault in NMIs though. Steve?
NMIs should be safe to fault after my patches went in. My main concern was with x86-64 as the NMI vector uses IST which resets the stack, but x86-32 keeps using the same stack if we are in ring0 (switches if we are in ring3 just like any other interrupt).
What's the original panic? I don't see the original post?
-- Steve
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