Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 07 Aug 2018 19:54:13 -0400
User-Agent: K-9 Mail for Android
In-Reply-To: <20180807194515.4e549c1a@gandalf.local.home>
References: <20180730222423.196630-1-joel@joelfernandes.org> <20180730222423.196630-4-joel@joelfernandes.org> <20180806155058.5ee875f4@gandalf.local.home> <CAJWu+oqvpev_EZC38_mi+UNRCxS8GqNVagHyGM4dUjruzKgwgQ@mail.gmail.com> <20180806214300.13e63523@gandalf.local.home> <CAJWu+oqZi2W9OYAn2xu17fdrBitQs4Gti4LxWmtx5B-EYtNMmA@mail.gmail.com> <20180807094954.5137972d@gandalf.local.home> <446AE5F2-39E0-46B6-8E0B-207E003DBF20@google.com> <20180807103410.4fe203cb@gandalf.local.home> <C1CB990F-8232-4168-89A8-E8C13B660B0B@google.com> <20180807110906.3a1b0ac4@gandalf.local.home> <6B9E5DC9-0859-41B4-9B72-A7D85E9EA2AD@google.com> <20180807194515.4e549c1a@gandalf.local.home>
MIME-Version: 1.0
Content-Type: text/plain;
 charset=utf-8
Content-Transfer-Encoding: quoted-printable
Subject: Re: [PATCH v12 3/3] tracing: Centralize preemptirq tracepoints and unify their usage
To:     Steven Rostedt <rostedt@goodmis.org>
CC:     Joel Fernandes <joel@joelfernandes.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "Cc: Android Kernel" <kernel-team@android.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Byungchul Park <byungchul.park@lge.com>,
        Ingo Molnar <mingo@redhat.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Glexiner <tglx@linutronix.de>,
        Tom Zanussi <tom.zanussi@linux.intel.com>
From:   Joel Fernandes <joelaf@google.com>
Message-ID: <6D0A3FD6-2190-4CC0-A3C0-7B3759E73243@google.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On August 7, 2018 7:45:15 PM EDT, Steven Rostedt <rostedt@goodmis=2Eorg> w=
rote:
>On Tue, 07 Aug 2018 11:24:13 -0400
>Joel Fernandes <joelaf@google=2Ecom> wrote:
>
>> On August 7, 2018 11:09:06 AM EDT, Steven Rostedt
><rostedt@goodmis=2Eorg> wrote:
>> >On Tue, 07 Aug 2018 10:48:05 -0400
>> >Joel Fernandes <joelaf@google=2Ecom> wrote:
>> > =20
>> >> >You mean if someone add a tracepoint callback to the irq disable
>> >> >tracepoint, and did a lockdep assert to make sure interrupts are
>> >> >disabled?   =20
>> >>=20
>> >> Yes that's what I meant=2E =20
>> >
>> >That sounds like a "Doctor, it hurts me when I do this" problem ;-)=20
>
>>=20
>> Haha, yes true=2E But just to clarify, I didn't do this to see the
>problem but noticed it with turning on existing things=2E :-) but I see
>your point=2E=2E=2E
>>=20
>
>OK, I hit this bug, but it's not because of the partial revert=2E This
>bug seems it needs to be another partial revert=2E I like you movement of
>the code, but I'm starting to doubt that we can use a trace event as a
>hook for critical areas yet=2E Well, not until we can use srcu in NMI=2E
>

I sent a patch to use srcu for all tracepoints including nmi=2E That patch=
 also removes this warning and fixes the one other issue masami reported (h=
ot plug causing a warning)=2E

If Paul and Mathieu can confirm SRCU works on offline CPUs that would be g=
reat=2E

It's just this one warning or anything else that makes you feel tracepoint=
s for critical paths isn't feasible?

Thanks=2E


>#define __DO_TRACE(tp, proto, args, cond, rcuidle)			\
>	do {								\
>		struct tracepoint_func *it_func_ptr;			\
>		void *it_func;						\
>		void *__data;						\
>		int __maybe_unused idx =3D 0;				\
>									\
>		if (!(cond))						\
>			return;						\
>									\
>		/* srcu can't be used from NMI */			\
>
>		WARN_ON_ONCE(rcuidle && in_nmi()); <=3D=3D WARN_ON_ONCE hit!
>
>WARNING: CPU: 3 PID: 3727 at
>/work/build/trace/nobackup/linux-test=2Egit/include/trace/events/preempti=
rq=2Eh:38
>trace_irq_disable_rcuidle+0x2a/0x6c
>Modules linked in: ip6t_REJECT nf_reject_ipv6 nf_conntrack_ipv6
>nf_defrag_ipv6 ip6table_filter ip6_tables ipv6 crc_ccitt r8169 ppdev
>parport_pc parport
>CPU: 3 PID: 3727 Comm: trace-cmd Not tainted 4=2E18=2E0-rc6-test+ #14
>Hardware name: MSI MS-7823/CSM-H87M-G43 (MS-7823), BIOS V1=2E6 02/22/2014
>EIP: trace_irq_disable_rcuidle+0x2a/0x6c
>Code: e9 01 00 00 00 c3 64 8b 0d 24 e1 50 c1 0f a3 0d e0 f1 3f c1 73 55
>55 89 e5 57 56 53 51 64 8b 0d cc 37 51 c1 0f ba e1 14 73 02 <0f> 0b 89
>d7 89 c6 b8 e0 d8 2e c1 e8 8e 5b fa ff 8b 1d 9c 27 3d c1=20
>EAX: c0401509 EBX: efa43680 ECX: 80110000 EDX: c0dc81f3
>ESI: ed823d44 EDI: efa43680 EBP: ed823cd0 ESP: ed823cc0
>DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 EFLAGS: 00010047
>CR0: 80050033 CR2: b7f06000 CR3: 30513b00 CR4: 001406f0
>Call Trace:
> trace_hardirqs_off_caller+0x23/0x2d
> trace_hardirqs_off_thunk+0xc/0x10
>EIP: default_do_nmi+0x1/0x157
>
>
>-- Steve

--=20
Sent from my Android device with K-9 Mail=2E Please excuse my brevity=2E