From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH V2 4/4] arm64: disable irq between breakpoint and step exception
Date: Tue, 25 Jul 2017 14:25:51 +0100 [thread overview]
Message-ID: <20170725132551.GB28815@arm.com> (raw)
In-Reply-To: <8f9c3073792c107e3d928e413499572ec75c5175.1499416107.git.panand@redhat.com>
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.
We'd probably be better off getting all users of kernel step (kprobes, kgdb
and perf) to run the step with irqs disabled, but I still have reservations
about that:
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?
Will
next prev parent reply other threads:[~2017-07-25 13:25 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-07 12:03 [PATCH V2 0/4] ARM64: Fix irq generation between breakpoint and step exception Pratyush Anand
2017-07-07 12:03 ` [PATCH V2 1/4] hw_breakpoint: Add step_needed event attribute Pratyush Anand
2017-07-25 13:27 ` Will Deacon
2017-07-25 14:14 ` Peter Zijlstra
2017-07-25 16:04 ` Mark Rutland
2017-07-26 5:42 ` Pratyush Anand
2017-07-26 7:49 ` Peter Zijlstra
2017-07-07 12:03 ` [PATCH V2 2/4] arm64: use hw_breakpoint_needs_single_step() to decide if step is needed Pratyush Anand
2017-07-07 12:03 ` [PATCH V2 3/4] hw-breakpoint: sample test: set step_needed bit field Pratyush Anand
2017-07-07 12:04 ` [PATCH V2 4/4] arm64: disable irq between breakpoint and step exception Pratyush Anand
2017-07-25 13:25 ` Will Deacon [this message]
2017-07-26 5:36 ` Pratyush Anand
2017-07-17 3:21 ` [PATCH V2 0/4] ARM64: Fix irq generation " Pratyush Anand
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