* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Fri, 16 Jan 2009, Ingo Molnar wrote: > > > > The sooner we start seeing these kinds of problems the better - > > delaying debug patches to after feature work is never a good idea - > > delaying feature changes works much better ;-) > > The problem with this particular debug feature is that when it finds > something, the machine usually just hangs because the interrupt handler > is just looping over reading some status register that returns 0xff, and > thinks that means "interrupt pending". > > Or maybe it's not looping, it's using some value as an index, or just > isn't ready to be called at all because it shut down things and as a > result it actually crashes with a NULL pointer dereference or something. > > And if you are in the middle of a resume, the result is not pretty. The > crash is often totally undebuggable. You can test it by using the > 'no_console_suspend' and 'acpi_sleep=s3_bios' kernel parameters, and > _maybe_ it will get things working. You're probably more likely to get a > working setup if you use VGA text mode rather than FBCON, though. > > In other words: the actual problems you hit tend to be very similar to > the nasty problems that DEBUG_SHIRQ can uncover - but with the _normal_ > DEBUG_SHIRQ you at least usually have a console, so you can add printk's > to see where it happened, and you get oopses etc. > > So I do think this is worth doing as a "make it easier to _see_ all the > nasty suspend/resume problems", but at the same time it's going to be > really really painful to debug, and it's not an option we can likely > ever enable in some distro kernel - because a regular user can't even > send a bug-report (just a "resume used to work, now it stopped working" > thing). Yeah, indeed. Perhaps a sysctl that turns it off by default might help? Under CONFIG_PM_DEBUG or so. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
