From: James Morse <james.morse@arm.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
"Paul E. McKenney" <paulmck@linux.ibm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org,
Naresh Kamboju <naresh.kamboju@linaro.org>,
Dan Rue <dan.rue@linaro.org>, Matt Hart <matthew.hart@linaro.org>,
Anders Roxell <anders.roxell@linaro.org>,
Daniel Diaz <daniel.diaz@linaro.org>
Subject: Re: [PATCH 3/3] arm64: debug: Remove rcu_read_lock from debug exception
Date: Fri, 19 Jul 2019 09:42:05 +0100 [thread overview]
Message-ID: <536ba068-50de-963e-c3a7-0440da56943a@arm.com> (raw)
In-Reply-To: <20190718233133.146065f668da6297e57e52ef@kernel.org>
Hi,
On 7/18/19 3:31 PM, Masami Hiramatsu wrote:
> On Thu, 18 Jul 2019 10:20:23 +0100
> Mark Rutland <mark.rutland@arm.com> wrote:
>
>> On Wed, Jul 17, 2019 at 11:22:15PM -0700, Paul E. McKenney wrote:
>>> On Thu, Jul 18, 2019 at 02:43:58PM +0900, Masami Hiramatsu wrote:
>>>> Remove rcu_read_lock()/rcu_read_unlock() from debug exception
>>>> handlers since the software breakpoint can be hit on idle task.
>>
>> Why precisely do we need to elide these? Are we seeing warnings today?
>
> Yes, unfortunately, or fortunately. Naresh reported that warns when
> ftracetest ran. I confirmed that happens if I probe on default_idle_call too.
>
> /sys/kernel/debug/tracing # echo p default_idle_call >> kprobe_events
> /sys/kernel/debug/tracing # echo 1 > events/kprobes/enable
> /sys/kernel/debug/tracing # [ 135.122237]
> [ 135.125035] =============================
> [ 135.125310] WARNING: suspicious RCU usage
> [ 135.132224] Call trace:
> [ 135.132491] dump_backtrace+0x0/0x140
> [ 135.132806] show_stack+0x24/0x30
> [ 135.133133] dump_stack+0xc4/0x10c
> [ 135.133726] lockdep_rcu_suspicious+0xf8/0x108
> [ 135.134171] call_break_hook+0x170/0x178
> [ 135.134486] brk_handler+0x28/0x68
> [ 135.134792] do_debug_exception+0x90/0x150
> [ 135.135051] el1_dbg+0x18/0x8c
> [ 135.135260] default_idle_call+0x0/0x44
> [ 135.135516] cpu_startup_entry+0x2c/0x30
> [ 135.135815] rest_init+0x1b0/0x280
> [ 135.136044] arch_call_rest_init+0x14/0x1c
> [ 135.136305] start_kernel+0x4d4/0x500
>>> The exception entry and exit use irq_enter() and irq_exit(), in this
>>> case, correct? Otherwise RCU will be ignoring this CPU.
>>
>> This is missing today, which sounds like the underlying bug.
>
> Agreed. I'm not so familier with how debug exception is handled on arm64,
> would it be a kind of NMI or IRQ?
Debug exceptions can interrupt both SError (think: machine check) and
pseudo-NMI, which both in turn interrupt interrupt-masked code. So they
are a kind of NMI. But, be careful not to call 'nmi_enter()' twice, see
do_serror() for how we work around this...
> Anyway, it seems that normal irqs are also not calling irq_enter/exit
> except for arch/arm64/kernel/smp.c
drivers/irqchip/irq-gic.c:gic_handle_irq() either calls
handle_domain_irq() or handle_IPI(). The enter/exit calls live in those
functions.
Thanks,
James
next prev parent reply other threads:[~2019-07-19 8:42 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-18 5:43 [PATCH 0/3] arm64: kprobes: Fix some bugs in arm64 kprobes Masami Hiramatsu
2019-07-18 5:43 ` [PATCH 1/3] arm64: kprobes: Recover pstate.D in single-step exception handler Masami Hiramatsu
2019-07-19 10:07 ` James Morse
2019-07-20 6:22 ` Masami Hiramatsu
2019-07-18 5:43 ` [PATCH 2/3] arm64: unwind: Prohibit probing on return_address() Masami Hiramatsu
2019-07-18 5:43 ` [PATCH 3/3] arm64: debug: Remove rcu_read_lock from debug exception Masami Hiramatsu
2019-07-18 6:22 ` Paul E. McKenney
2019-07-18 9:20 ` Mark Rutland
2019-07-18 14:31 ` Masami Hiramatsu
2019-07-19 8:42 ` James Morse [this message]
2019-07-20 7:32 ` Masami Hiramatsu
2019-07-21 1:50 ` Masami Hiramatsu
2019-07-19 9:59 ` Mark Rutland
2019-07-20 7:54 ` Masami Hiramatsu
2019-07-24 10:45 ` Mark Rutland
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=536ba068-50de-963e-c3a7-0440da56943a@arm.com \
--to=james.morse@arm.com \
--cc=anders.roxell@linaro.org \
--cc=catalin.marinas@arm.com \
--cc=dan.rue@linaro.org \
--cc=daniel.diaz@linaro.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=matthew.hart@linaro.org \
--cc=mhiramat@kernel.org \
--cc=naresh.kamboju@linaro.org \
--cc=paulmck@linux.ibm.com \
--cc=will.deacon@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
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;
as well as URLs for NNTP newsgroup(s).