From: Masami Hiramatsu <mhiramat@kernel.org>
To: James Morse <james.morse@arm.com>
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: Sat, 20 Jul 2019 16:32:32 +0900 [thread overview]
Message-ID: <20190720163232.49f80bc0e53afb893e7a82e6@kernel.org> (raw)
In-Reply-To: <536ba068-50de-963e-c3a7-0440da56943a@arm.com>
Hi James,
On Fri, 19 Jul 2019 09:42:05 +0100
James Morse <james.morse@arm.com> wrote:
> 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...
OK. I think we can use rcu_nmi_enter/exit() as same as x86.
> > 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.
Ah, I see.
Would you think we need to put rcu_nmi_enter/exit() as similar to x86
on do_mem_abort() and do_sp_pc_abort() too?
Thank you,
--
Masami Hiramatsu <mhiramat@kernel.org>
next prev parent reply other threads:[~2019-07-20 7:32 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
2019-07-20 7:32 ` Masami Hiramatsu [this message]
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
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