On Thu, 6 Aug 2020 at 18:06, Marco Elver <el...@google.com> wrote: > On Thu, 6 Aug 2020 at 15:17, Marco Elver <el...@google.com> wrote: > > On Thu, Aug 06, 2020 at 01:32PM +0200, pet...@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-el...@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. :-/ Thanks, -- Marco
