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.)
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. I also get some "BUG: MAX_LOCKDEP_CHAINS too low!" on syzbot (KCSAN is not in the stacktrace). Although it may be unrelated: https://lore.kernel.org/lkml/[email protected]/ -- when are they expected? Thanks, -- Marco
