From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v8 3/4] arm64: Add do_softirq_own_stack() and enable irq_stacks
Date: Wed, 9 Dec 2015 11:38:53 +0000 [thread overview]
Message-ID: <20151209113852.GC9303@arm.com> (raw)
In-Reply-To: <5667F897.5070005@arm.com>
On Wed, Dec 09, 2015 at 09:47:03AM +0000, James Morse wrote:
> On 08/12/15 17:23, James Morse wrote:
> > My only theory is that there is an off by one, and its reading what was
> > x29 instead. This wouldn't show up in these tests, but might be a
> > problem for aarch32 user-space, as presumably x29==0 when it switches to
> > aarch64 mode for el0_irq(). I will try this tomorrow.
>
> Yup, this is what is happening. Its an off-by-one due to broken thinking
> about how the stack works. My broken thinking was:
>
> > top ------------
> > | dummy_lr | <- irq_stack_ptr
> > ------------
> > | x29 |
> > ------------
> > | x19 | <- irq_stack_ptr - 0x10
> > ------------
> > | xzr |
> > ------------
>
> But the stack-pointer is decreased before use. So it actually looks like
> this:
>
> > ------------
> > | | <- irq_stack_ptr
> > top ------------
> > | dummy_lr |
> > ------------
> > | x29 | <- irq_stack_ptr - 0x10
> > ------------
> > | x19 |
> > ------------
> > | xzr | <- irq_stack_ptr - 0x20
> > ------------
>
> The value being used as the original stack is x29, which in all the
> tests is sp but without the current frames data, hence there are no
> missing frames in the output.
>
> Jungseok Lee picked it up with a 32bit user space because aarch32 can't
> use x29, so it remains 0 forever. The fix he posted is correct.
>
> Will: do you want to take Jungseok Lee's patch as a 'Fixes:', or is it
> easier if I repost the series?
I'll take it as a fix on top, but I still want to get to the bottom of
why unwind_frame appeared to be exploding. We really shouldn't be relying
on the frame layout to provide us with safe addresses in there.
Will
next prev parent reply other threads:[~2015-12-09 11:38 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-04 11:02 [PATCH v8 0/4] arm64: Add support for IRQ stack James Morse
2015-12-04 11:02 ` [PATCH v8 1/4] arm64: Store struct task_info in sp_el0 James Morse
2015-12-04 13:27 ` Catalin Marinas
2015-12-04 14:55 ` James Morse
2015-12-04 16:18 ` Catalin Marinas
2015-12-06 13:15 ` Jungseok Lee
2015-12-04 11:02 ` [PATCH v8 2/4] arm64: Modify stack trace and dump for use with irq_stack James Morse
2015-12-04 12:21 ` Jungseok Lee
2015-12-04 14:31 ` Catalin Marinas
2015-12-04 11:02 ` [PATCH v8 3/4] arm64: Add do_softirq_own_stack() and enable irq_stacks James Morse
2015-12-04 13:46 ` Catalin Marinas
2015-12-04 13:47 ` Catalin Marinas
2015-12-07 22:48 ` Catalin Marinas
2015-12-08 11:43 ` Will Deacon
2015-12-08 16:02 ` Jungseok Lee
2015-12-08 17:23 ` James Morse
2015-12-08 17:27 ` Will Deacon
2015-12-08 23:13 ` Jungseok Lee
2015-12-09 9:47 ` James Morse
2015-12-09 11:38 ` Will Deacon [this message]
2015-12-09 13:45 ` Will Deacon
2015-12-09 14:36 ` James Morse
2015-12-04 11:02 ` [PATCH v8 4/4] arm64: switch to irq_stack during softirq James Morse
2015-12-04 14:01 ` Catalin Marinas
2015-12-04 14:39 ` James Morse
2015-12-04 18:40 ` Catalin Marinas
2015-12-08 10:29 ` James Morse
2015-12-06 13:51 ` Jungseok Lee
2015-12-04 12:17 ` [PATCH v8 0/4] arm64: Add support for IRQ stack Jungseok Lee
2015-12-06 13:56 ` Jungseok Lee
2015-12-04 13:57 ` Catalin Marinas
2015-12-06 13:33 ` Jungseok Lee
2015-12-10 10:22 ` [PATCH v8 5/4] arm64: Fix off-by-one in stack tracing when stepping off irq stack James Morse
2015-12-10 10:22 ` [PATCH v8 6/4] arm64: Add this_cpu_ptr() assembler macro for use in entry.S James Morse
2015-12-10 10:22 ` [PATCH v8 7/4] arm64: when walking onto the task stack, check sp & fp are in current->stack James Morse
2015-12-10 10:22 ` [PATCH v8 8/4] arm64: don't call C code with el0's fp register James Morse
2015-12-10 14:03 ` [PATCH v8 5/4] arm64: Fix off-by-one in stack tracing when stepping off irq stack Jungseok Lee
2015-12-15 11:21 ` [PATCH v8 9/4] arm64: reduce stack use in irq_handler James Morse
2015-12-18 16:01 ` [PATCH v8 9/4] arm64: remove irq_count and do_softirq_own_stack() James Morse
2015-12-20 11:07 ` Jungseok Lee
2015-12-21 11:30 ` Will Deacon
2015-12-21 12:19 ` James Morse
2015-12-21 12:21 ` Will Deacon
2015-12-21 14:06 ` Jungseok Lee
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20151209113852.GC9303@arm.com \
--to=will.deacon@arm$(echo .)com \
--cc=linux-arm-kernel@lists$(echo .)infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox