On Thu, 27 Feb 2014, H. Peter Anvin wrote: > On 02/27/2014 03:30 PM, Steven Rostedt wrote: > > On Thu, 27 Feb 2014 14:52:54 -0800 > > "H. Peter Anvin" <h...@zytor.com> wrote: > > > >> On 02/27/2014 02:31 PM, Steven Rostedt wrote: > >>> > >>> Yeah, something is getting mesed up. > >>> > >> > >> What it *looks* like to me is that we try to nest the cr2 save/restore, > >> which doesn't nest because it is a percpu variable. > >> > >> ... except in the x86-64 case, we *ALSO* save/restore cr2 inside > >> entry_64.S, which makes the stuff in do_nmi completely redundant and > >> there for no good reason. > > > > Peter, look at the code. That percpu cr2 is in a #ifdef CONFIG_X86_32 > > section. That is, it isn't even executed. That's i386 code. The only > > place the cr2 is saved for x86_64 is in entry_64.S. > > > > Right, egg on my face. However, I still think it would make more sense > for it to nest the way entry_64.S does if at all possible. > > That makes this even more confusing, though. I would still like to see > what happens with the patch I sent Vince.
I'll try your patch momentarily, first I had some other changes I started running before I left work (for some reason it recompiled the whole kernel). 8: function: perf_output_begin 8: bprint: perf_output_begin: VMW: event type 2 config 2a st: 2c3e 8: bputs: perf_output_begin: VMW: before rcu_dereference 9: function: __do_page_fault 9: function: down_read_trylock 9: function: _cond_resched 9: function: find_vma so it looks like the fault happens rcu_read_lock(); 116 /* 117 * For inherited events we send all the output towards the parent. 118 */ 119 if (event->parent) 120 event = event->parent; 121 somewhere between here 122 rb = rcu_dereference(event->rb); 123 if (unlikely(!rb)) 124 goto out; and here 125 126 if (unlikely(!rb->nr_pages)) 127 goto out; although if rcu locks do anything to turn off tracing then this could be suspect. Vince -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
