Messages in this thread | | | Subject | Re: [PATCH] x86/paravirt: Add missing noinstr to arch_local*() helpers | From | Jürgen Groß <> | Date | Fri, 7 Aug 2020 12:35:21 +0200 |
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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 <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
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 think CONFIG_PARAVIRT_XXL shouldn't matter, but I'm not completely sure about that. CONFIG_PARAVIRT_SPINLOCKS would be my primary suspect.
Juergen
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