linux-kernel - [RFC][PATCH 0/3] x86/nmi: Print all cpu stacks from NMI safely

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Message-Id: <20140619213329.478113470@goodmis.org>
Date:	Thu, 19 Jun 2014 17:33:29 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	linux-kernel@...r.kernel.org
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>, Michal Hocko <mhocko@...e.cz>,
	Jan Kara <jack@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Dave Anderson <anderson@...hat.com>,
	Petr Mladek <pmladek@...e.cz>
Subject: [RFC][PATCH 0/3] x86/nmi: Print all cpu stacks from NMI safely

This is my proposal to print the NMI stack traces from an RCU stall safely.
Here's the gist of it.

Patch 1: move the trace_seq out of the tracing code. It's useful for other
 purposes too. Like writing from an NMI context.

Patch 2: Add a per_cpu "printk_func" that printk calls. By default it calls
 vprintk_def() which does what it has always done. This allows us to
 override what printk() calls normally on a per cpu basis.

Patch 3: Have the NMI handler that dumps the stack trace just change the
 printk_func to call a NMI safe printk function that writes to a per cpu
 trace_seq. When all NMI handlers chimed in, the original caller prints
 out the trace_seqs for each CPU from a printk safe context.

This is much less intrusive than the other versions out there.

Note, The biggest change was the moving of trace_seq code out of trace_output.c
and into the new trace_seq.c library.

Thoughts?

Steven Rostedt (Red Hat) (3):
      trace_seq: Move the trace_seq code to lib/
      printk: Add per_cpu printk func to allow printk to be diverted
      x86/nmi: Perform a safe NMI stack trace on all CPUs

----
 arch/x86/kernel/apic/hw_nmi.c |  66 ++++++++-
 include/linux/percpu.h        |   3 +
 include/linux/printk.h        |   2 +
 include/linux/trace_seq.h     |  68 ++--------
 kernel/printk/printk.c        |  38 ++++--
 kernel/trace/trace.c          |  24 ----
 kernel/trace/trace_output.c   | 268 -------------------------------------
 kernel/trace/trace_output.h   |  16 ---
 lib/Makefile                  |   2 +-
 lib/trace_seq.c               | 303 ++++++++++++++++++++++++++++++++++++++++++
 10 files changed, 412 insertions(+), 378 deletions(-)
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