linux-kernel - RE: [RFC][PATCH v3 2/3] Skip spin_locks in panic case and add WARN

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Message-ID: <0207C53569FE594381A4F2EB66570B2A018EFB83C4@orsmsx508.amr.corp.intel.com>
Date:	Mon, 12 Dec 2011 10:48:52 -0800
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Seiji Aguchi <seiji.aguchi@....com>,
	Don Zickus <dzickus@...hat.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Matthew Garrett <mjg@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	"Chen, Gong" <gong.chen@...el.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"Brown, Len" <len.brown@...el.com>,
	"'ying.huang@...el.com'" <'ying.huang@...el.com'>,
	"'ak@...ux.intel.com'" <'ak@...ux.intel.com'>,
	"'hughd@...omium.org'" <'hughd@...omium.org'>,
	"'mingo@...e.hu'" <'mingo@...e.hu'>,
	"jmorris@...ei.org" <jmorris@...ei.org>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"namhyung@...il.com" <namhyung@...il.com>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Satoru Moriya <satoru.moriya@....com>
Subject: RE: [RFC][PATCH v3 2/3] Skip spin_locks in panic case and add
 WARN_ON()

> if (reason == KMSG_DUMP_PANIC) {
> 	if(is_spin_locked(&psinfo->buf_lock))
> 		pr_err("lock is taken.\n");
> else {
> 	spin_lock_irqsave(&psinfo->buf_lock, flags);
> }
>
> However, this won't work for this reason.
>  - printk() must not be called in serialized path because deadlock of logbuf_lock may cause.

There is also the issue that kmsg has already computed the addresses
of useful pieces in __log_buf at this point - so any printk() we
add here is not going to be saved into pstore.  So a user relying
on pstore to see what happened, won't see any messages we add here.

-Tony
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