Re: [PATCH v12 3/3] tracing: Centralize preemptirq tracepoints and unify their usage

From: Steven Rostedt <rostedt@goodmis.org>
To: Joel Fernandes <joelaf@google.com>
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>
Subject: Re: [PATCH v12 3/3] tracing: Centralize preemptirq tracepoints and unify their usage
Date: Tue, 7 Aug 2018 19:45:15 -0400	[thread overview]
Message-ID: <20180807194515.4e549c1a@gandalf.local.home> (raw)
In-Reply-To: <6B9E5DC9-0859-41B4-9B72-A7D85E9EA2AD@google.com>

On Tue, 07 Aug 2018 11:24:13 -0400
Joel Fernandes <joelaf@google.com> wrote:

> On August 7, 2018 11:09:06 AM EDT, Steven Rostedt <rostedt@goodmis.org> wrote:
> >On Tue, 07 Aug 2018 10:48:05 -0400
> >Joel Fernandes <joelaf@google.com> wrote:
> >  
> >> >You mean if someone add a tracepoint callback to the irq disable
> >> >tracepoint, and did a lockdep assert to make sure interrupts are
> >> >disabled?    
> >> 
> >> Yes that's what I meant.  
> >
> >That sounds like a "Doctor, it hurts me when I do this" problem ;-)  
> 
> Haha, yes true. But just to clarify, I didn't do this to see the problem but noticed it with turning on existing things. :-) but I see your point...
> 

OK, I hit this bug, but it's not because of the partial revert. This
bug seems it needs to be another partial revert. 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. Well, not until we can use srcu in NMI.

#define __DO_TRACE(tp, proto, args, cond, rcuidle)			\
	do {								\
		struct tracepoint_func *it_func_ptr;			\
		void *it_func;						\
		void *__data;						\
		int __maybe_unused idx = 0;				\
									\
		if (!(cond))						\
			return;						\
									\
		/* srcu can't be used from NMI */			\

		WARN_ON_ONCE(rcuidle && in_nmi()); <== WARN_ON_ONCE hit!

WARNING: CPU: 3 PID: 3727 at /work/build/trace/nobackup/linux-test.git/include/trace/events/preemptirq.h: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 4.18.0-rc6-test+ #14
Hardware name: MSI MS-7823/CSM-H87M-G43 (MS-7823), BIOS V1.6 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 
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