linux-kernel - [RFC][PATCH v3 0/3] Make pstore/kmsg_dump run after stopping other cpus in panic path

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Date:	Fri, 2 Dec 2011 17:08:32 -0500
From:	Seiji Aguchi <seiji.aguchi@....com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Luck, Tony" <tony.luck@...el.com>,
	Don Zickus <dzickus@...hat.com>,
	Matthew Garrett <mjg@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	"Chen, Gong" <gong.chen@...el.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"len.brown@...el.com" <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>
CC:	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Satoru Moriya <satoru.moriya@....com>
Subject: [RFC][PATCH v3 0/3] Make pstore/kmsg_dump run after stopping other
 cpus in panic path

Hi,

Discussion:
 As Don mentioned in following thread, it would be nice for pstore/kmsg_dump to serialize 
 panic path because they can log messages reliably.

 https://lkml.org/lkml/2011/10/13/427

 This patchset is based on his proposal switching smp_send_stop() from REBOOT_VECTOR to NMI.

Change Log:

 v2 -> v3
   - Skip spin_locks in panic case in both kmsg_dump() and pstore_dump() instead of calling spin_lock_init()
     to avoid potential issues due to spin_lock_init()
   - Add WARN_ON() in "in_nmi() and !panic" case into kmsg_dump() so that we trap when someone adds 
     new kmsg_dump() in NMI path in the future
   - Skip subsequent kmsg_dump() function calls to avoid deadlock.

 v1 -> v2
  - Add trylocks to kmsg_dump()/pstore_dump() so that they can work in NMI context.  
  - Divide a patch into two
     First one is just moving kmsg_dump(KMSG_DUMP_PANIC) below smp_send_stop()
     Second one is changing lock operations in kmsg_dump()/pstore_dump()
 v1
  - Move kmsg_dump(KMSG_DUMP_PANIC) below smp_send_stop
  - Bust logbuf_lock of kmsg_dump() in panic path for avoiding deadlock
  - Bust psinfo->buf_lock of pstore_dump() in panic path for avoiding deadlock

Patch Description:
   [RFC][PATCH v3 1/3] Move kmsg_dump(KMSG_DUMP_PANIC) below smp_send_stop()
     - Just move kmsg_dump(KMSG_DUMP_PANIC) below smp_send_stop()

   [RFC][PATCH v3 2/3] Skip spin_locks in panic case and add WARN_ON()
     - Skip spin_locks in panic case in both kmsg_dump() and pstore_dump()
     - Add WARN_ON() in "in_nmi() and !panic" case into kmsg_dump()

   [RFC][PATCH v3 3/3] Skip subsequent kmsg_dump()
     - Skip subsequent kmsg_dump() function calls

TODO:
 This patchset focuses on only kmsg_dump()/pstore_dump().
 So, we have to check whether backend drivers work.

Any comments are welcome.

Seiji Aguchi (3):
 Move kmsg_dump(KMSG_DUMP_PANIC) below smp_send_stop()
 Skip spin_locks in panic case and add WARN_ON()
 Skip subsequent kmsg_dump()

 fs/pstore/platform.c |   16 ++++++----------
 kernel/panic.c       |    4 ++--
 kernel/printk.c      |   23 +++++++++++++++++++++--
 3 files changed, 29 insertions(+), 14 deletions(-)
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