On Fri, Aug 07, 2020 at 12:35PM +0200, Jürgen Groß wrote: > On 07.08.20 11:50, Marco Elver wrote: > > 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 <[email protected]> wrote: > > > > > On Thu, 6 Aug 2020 at 15:17, Marco Elver <[email protected]> wrote: > > > > > > On Thu, Aug 06, 2020 at 01:32PM +0200, [email protected] 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/[email protected] > > > > > > > > > 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 > > Anything special I need to do to reproduce the problem? Or would you be > willing to do some more rounds with different config settings?
I can only test it with syzkaller, but that probably doesn't help if you don't already have it set up. It can't seem to find a C reproducer. I did some more rounds with different configs. > I think CONFIG_PARAVIRT_XXL shouldn't matter, but I'm not completely > sure about that. CONFIG_PARAVIRT_SPINLOCKS would be my primary suspect. Yes, PARAVIRT_XXL doesn't make a different. When disabling PARAVIRT_SPINLOCKS, however, the warnings go away. Thanks, -- Marco
