linux-kernel - Tracing IRQ-flags

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Date:	Sun, 27 Sep 2015 15:25:41 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Ingo Molnar <mingo@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Jiri Kosina <jikos@...nel.org>, Tejun Heo <tj@...nel.org>,
	Lai Jiangshan <laijs@...fujitsu.com>
Subject: Tracing IRQ-flags

Hi Ingo, Hi Steven,

I am still fighting with a llvmlinux problem in the area...

    workqueue | hid | irq-flags (hardirqs/sofirqs disabled) | whatever?!

...(see [0]).

[   24.705463] BUG: sleeping function called from invalid context at
kernel/workqueue.c:2680
[   24.705576] in_atomic(): 0, irqs_disabled(): 1, pid: 1447, name: acpid

Several people had ideas where to look at - Thanks.

Finally, Jiri encouraged me to try with a ftrace graph trace (see [1]).

I remembered TraceFS entered Linux v4.1 and wanted to play with it.
One result is the attached doc.

Can I do a ftrace graph trace with TraceFS?
And how do I do that?

Steven, is it possible to place your tracing mini-HOWTO (file:
/sys/kernel/tracing/README) into docs-dir?
Existing Documentation/trace?
Documentation/tracefs (new)?
Documentation/tracing (new)?
First, I was confused how and where to mount tracefs :-(.
Thanks.

Ingo, the kernel-configs in irqflags-tracing.txt doc are a bit outdated.
Which are very important for irqflags-tracing (hardirq | softirq)?
Are the lockdeps settings important?
Is irqsoff setting important?

$ egrep -i 'lockdep|tracing|irqsoff|irqflags' /boot/config-$(uname -r) | sort
CONFIG_DEBUG_LOCKDEP=y
CONFIG_EVENT_TRACING=y
CONFIG_IRQSOFF_TRACER=y
CONFIG_IWLWIFI_DEVICE_TRACING=y
CONFIG_LOCKDEP_SUPPORT=y
CONFIG_LOCKDEP=y
# CONFIG_MAC80211_MESSAGE_TRACING is not set
CONFIG_TRACE_IRQFLAGS_SUPPORT=y
CONFIG_TRACE_IRQFLAGS=y
CONFIG_TRACING_SUPPORT=y
CONFIG_TRACING=y

What about a new tracing-dir in Documentation/ and place all tracing docs there?

Thanks.

Regards,
- Sedat -

[0] http://marc.info/?t=144179442100006&r=1&w=2
[1] http://marc.info/?l=linux-kernel&m=144318685710847&w=2
[2] https://lwn.net/Articles/631798/
[3] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/irqflags-tracing.txt

View attachment "TRACEFS-TRACING-IRQFLAGS.txt" of type "text/plain" (3058 bytes)

View attachment "tracefs-tracing-mini-HOWTO.txt" of type "text/plain" (5257 bytes)