Messages in this thread | | | Date | Fri, 11 May 2018 09:37:16 -0400 | From | Steven Rostedt <> | Subject | Re: printk feature for syzbot? |
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On Fri, 11 May 2018 18:50:04 +0900 Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> wrote:
> On (05/11/18 11:17), Dmitry Vyukov wrote: > > > > From what I see, it seems that interrupts can be nested: > > Hm, I thought that in general IRQ handlers run with local IRQs > disabled on CPU. So, generally, IRQs don't nest. Was I wrong? > NMIs can nest, that's true; but I thought that at least IRQs > don't.
We normally don't run nested interrupts, although as the comment in preempt.h says:
* The hardirq count could in theory be the same as the number of * interrupts in the system, but we run all interrupt handlers with * interrupts disabled, so we cannot have nesting interrupts. Though * there are a few palaeontologic drivers which reenable interrupts in * the handler, so we need more than one bit here.
And no, NMI handlers do not nest. Yes, we deal with nested NMIs, but in those cases, we just set a bit as a latch, and return, and when the first NMI is complete, it checks that bit and if it is set, it executes another NMI handler.
> > > https://syzkaller.appspot.com/bug?id=72eddef9cedcf81486adb9dd3e789f0d77505ba5 > > https://syzkaller.appspot.com/bug?id=66fcf61c65f8aa50bbb862eb2fde27c08909a4ff > > > > Will this in_nmi()/in_irq()/in_serving_softirq()/else be enough to > > untangle output printed by such nested interrupts? > > Well, hm. __irq_enter() does preempt_count_add(HARDIRQ_OFFSET) and > __irq_exit() does preempt_count_sub(HARDIRQ_OFFSET). So, technically, > you can store > > preempt_count() & HARDIRQ_MASK > preempt_count() & SOFTIRQ_MASK > preempt_count() & NMI_MASK > > in that extended context tracking. The numbers will not tell you > the IRQ line number, for instance, but at least you'll be able to > distinguish different hard/soft IRQs, NMIs. Just an idea, I didn't > check it, may be it won't work at all. > > Ideally, the serial log should be like this > > i:1 ... foo() > i:1 ... bar() > i:2 ... foo() // __irq_enter() > i:2 ... bar() > i:2 ... buz() // __irq_exit() > i:1 ... buz() > > but I may be completely wrong. > > Petr and Steven probably will have better ideas.
I handle nesting of different contexts in the ftrace ring buffer using the preempt count. See trace_recursive_lock/unlock() in kernel/trace/ring_buffer.c.
-- Steve
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