On Fri, 28 Feb 2014 12:34:05 -0800 "Paul E. McKenney" <paul...@linux.vnet.ibm.com> wrote:
> On Thu, Feb 27, 2014 at 08:00:04PM -0500, Vince Weaver wrote: > > 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. > > The most likely suspect is of course event->rb in the rcu_dereference. > I have to defer to Steven on how rcu_read_lock() and rcu_read_unlock() > currently interact with tracing. ;-) These are all perf related. You'll need to defer to Peter Zijlstra ;-) -- Steve -- 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/