linux-kernel - Re: 3.14-rc2 XFS backtrace because irqs

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Message-ID: <20140212081333.GC7984@mtj.dyndns.org>
Date:	Wed, 12 Feb 2014 03:13:33 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dave Chinner <david@...morbit.com>, Jens Axboe <axboe@...nel.dk>,
	Steven Rostedt <rostedt@...dmis.org>,
	Dave Jones <davej@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Eric Sandeen <sandeen@...deen.net>,
	Linux Kernel <linux-kernel@...r.kernel.org>, xfs@....sgi.com
Subject: Re: 3.14-rc2 XFS backtrace because irqs_disabled.

On Tue, Feb 11, 2014 at 10:59:58PM -0800, Linus Torvalds wrote:
> There's a lot of 200+ byte stack frames in block/blk-core.s, and they
> all seem to be of the type perf_trace_block_buffer() - things created
> with DECLARE_EVENT_CLASS(), afaik. Why they all have 200+ bytes of
> frame, I have no idea. That sounds like a potential disaster too,
> although hopefully it's mostly leaf functions - but leaf functions
> *deep* in the callchain. Tejun? Steven, why _do_ they end up with such
> huge frames?

It looks like they're essentially the same for all the automatically
generated trace functions.  I'm seeing 232 byte stack frame in most of
them.  If I'm not completely confused by these macros, these are
generated by DECLARE_EVENT_CLASS() in include/trace/ftrace.h and
contains struct pt_regs in the stack frame which is already 168 bytes,
so that seems like the culprit.  No idea whether this is something
avoidable.  At least they shouldn't nest in any way.  Steven?

Thanks.

-- 
tejun
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