On Fri, Aug 07, 2020 at 11:24AM +0200, Jürgen Groß wrote:
> On 07.08.20 11:01, Marco Elver wrote:
> > On Thu, 6 Aug 2020 at 18:06, Marco Elver <elver@google.com> wrote:
> > > On Thu, 6 Aug 2020 at 15:17, Marco Elver <elver@google.com> wrote:
> > > > On Thu, Aug 06, 2020 at 01:32PM +0200, peterz@infradead.org wrote:
> > > > > On Thu, Aug 06, 2020 at 09:47:23AM +0200, Marco Elver wrote:
> > > > > > Testing my hypothesis that raw then nested non-raw
> > > > > > local_irq_save/restore() breaks IRQ state tracking -- see the reproducer
> > > > > > below. This is at least 1 case I can think of that we're bound to hit.
> > > > ...
> > > > > 
> > > > > /me goes ponder things...
> > > > > 
> > > > > How's something like this then?
> > > > > 
> > > > > ---
> > > > >   include/linux/sched.h |  3 ---
> > > > >   kernel/kcsan/core.c   | 62 ++++++++++++++++++++++++++++++++++++---------------
> > > > >   2 files changed, 44 insertions(+), 21 deletions(-)
> > > > 
> > > > Thank you! That approach seems to pass syzbot (also with
> > > > CONFIG_PARAVIRT) and kcsan-test tests.
> > > > 
> > > > I had to modify it some, so that report.c's use of the restore logic
> > > > works and not mess up the IRQ trace printed on KCSAN reports (with
> > > > CONFIG_KCSAN_VERBOSE).
> > > > 
> > > > I still need to fully convince myself all is well now and we don't end
> > > > up with more fixes. :-) If it passes further testing, I'll send it as a
> > > > real patch (I want to add you as Co-developed-by, but would need your
> > > > Signed-off-by for the code you pasted, I think.)
> > 
> > I let it run on syzbot through the night, and it's fine without
> > PARAVIRT (see below). I have sent the patch (need your Signed-off-by
> > as it's based on your code, thank you!):
> > https://lkml.kernel.org/r/20200807090031.3506555-1-elver@google.com
> > 
> > > With CONFIG_PARAVIRT=y (without the notrace->noinstr patch), I still
> > > get lockdep DEBUG_LOCKS_WARN_ON(!lockdep_hardirqs_enabled()), although
> > > it takes longer for syzbot to hit them. But I think that's expected
> > > because we can still get the recursion that I pointed out, and will
> > > need that patch.
> > 
> > Never mind, I get these warnings even if I don't turn on KCSAN
> > (CONFIG_KCSAN=n). Something else is going on with PARAVIRT=y that
> > throws off IRQ state tracking. :-/
> 
> What are the settings of CONFIG_PARAVIRT_XXL and
> CONFIG_PARAVIRT_SPINLOCKS in this case?

I attached a config.

	$> grep PARAVIRT .config
	CONFIG_PARAVIRT=y
	CONFIG_PARAVIRT_XXL=y
	# CONFIG_PARAVIRT_DEBUG is not set
	CONFIG_PARAVIRT_SPINLOCKS=y
	# CONFIG_PARAVIRT_TIME_ACCOUNTING is not set
	CONFIG_PARAVIRT_CLOCK=y

Thanks,
-- Marco