Messages in this thread | | | Subject | Re: [PATCH V2 4/4] arm64: disable irq between breakpoint and step exception | From | Pratyush Anand <> | Date | Wed, 26 Jul 2017 11:06:02 +0530 |
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Hi Will,
Thanks for your review.
On Tuesday 25 July 2017 06:55 PM, Will Deacon wrote: > On Fri, Jul 07, 2017 at 05:34:00PM +0530, Pratyush Anand wrote: >> If an interrupt is generated between breakpoint and step handler then >> step handler can not get correct step address. This situation can easily >> be invoked by samples/hw_breakpoint/data_breakpoint.c. It can also be >> reproduced if we insert any printk() statement or dump_stack() in perf >> overflow_handler. So, it seems that perf is working fine just luckily. >> If the CPU which is handling perf breakpoint handler receives any >> interrupt then, perf step handler will not execute sanely. >> >> This patch improves do_debug_exception() handling, which enforces now, >> that exception handler function: >> - should return 0 for any software breakpoint and hw >> breakpoint/watchpoint handler if it does not expect a single step stage >> - should return 1 if it expects single step. >> - A single step handler should always return 0. >> - All handler should return a -ve error in any other case. >> >> Now, we can know in do_debug_exception() that whether a step exception >> will be followed or not. If there will a step exception then disable >> irq. Re-enable it after single step handling. > > AFAICT, this is only a problem for kernel-mode breakpoints where we end up > stepping into the interrupt handler when trying to step over a breakpoint.
I think yes.
> > We'd probably be better off getting all users of kernel step (kprobes, kgdb > and perf) to run the step with irqs disabled,
That should be doable. We can easily manage all of them in do_debug_exception() if individual brk handlers return correct value as per the rule mentioned in the commit log of this patch.
I think, I can take care of kprobes and kgdb as well in next version of patch.
> but I still have reservations > about that:
So, IIUC, you have concern about faulting of a instruction being stepped. Since we will have a notion of *irq_en_needed*, so I think, if needed we can re-enable interrupt in fault handler do_mem_abort().
Whats your opinion here?
> > http://lists.infradead.org/pipermail/linux-arm-kernel/2017-May/508066.html > http://lists.infradead.org/pipermail/linux-arm-kernel/2017-June/510814.html > > Wouldn't it be better to follow kprobes/kgdb and have perf run the step with > irqs disabled? -- Regards Pratyush
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