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From: Thomas Gleixner <tglx@linutronix.de>
To: Dongdong Deng <libfetion@gmail.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Jason Wessel <jason.wessel@windriver.com>,
	linux-kernel@vger.kernel.org,
	kgdb-bugreport@lists.sourceforge.net, mingo@elte.hu,
	John Stultz <johnstul@us.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Magnus Damm <damm@igel.co.jp>
Subject: Re: [PATCH 3/4] kgdb,clocksource: Prevent kernel hang in kernel debugger
Date: Tue, 26 Jan 2010 12:16:41 +0100 (CET)	[thread overview]
Message-ID: <alpine.LFD.2.00.1001261204100.5926@localhost.localdomain> (raw)
In-Reply-To: <alpine.LFD.2.00.1001261108410.5926@localhost.localdomain>

On Tue, 26 Jan 2010, Thomas Gleixner wrote:
> There is no sane way to reliably prevent TSC from becoming unstable
> when kgdb stops the kernel inside the watchdog code. And I do not care
> about that at all.
> 
> I'm not going to clutter code with crazy workarounds just because some
> people believe that using a kernel debugger is a good idea. If people
> insist on using kgdb then the possible "TSC becomes unstable" side
> effect is the least of their problems.

Btw, if the kernel uses tick based timekeeping or a clock source which
wraps in rather short intervals (e.g. pm-timer wraps after ~4.6
seconds), stopping the kernel with kgdb will inevitably screw up time
keeping anyway.

So there is really no reason to worry about TSC becoming unstable.

There is only one real sensible solution for this:

 Do _not_ use kgdb - which is the modus operandi of every sane kernel
 developer on the planet.

Thanks,

	tglx

  reply	other threads:[~2010-01-26 11:17 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-01-26  4:26 [PATCH 0/4] kgdb regression fixes for 2.6.33 Jason Wessel
2010-01-26  4:26 ` [PATCH 1/4] x86,hw_breakpoint,kgdb: kgdb to use hw_breakpoint API Jason Wessel
2010-01-28 17:10   ` Frederic Weisbecker
2010-01-28 17:44     ` [PATCH 1/4] x86,hw_breakpoint,kgdb: kgdb to use hw_breakpointAPI Jason Wessel
2010-01-28 19:58       ` Jason Wessel
2010-01-28 20:17         ` Frederic Weisbecker
2010-01-28 20:23           ` [PATCH 1/4] x86,hw_breakpoint,kgdb: kgdb to usehw_breakpointAPI Jason Wessel
2010-01-28 21:54             ` Frederic Weisbecker
2010-01-28 20:04       ` [PATCH 1/4] x86,hw_breakpoint,kgdb: kgdb to use hw_breakpointAPI Frederic Weisbecker
2010-01-28 20:27         ` [PATCH 1/4] x86,hw_breakpoint,kgdb: kgdb to usehw_breakpointAPI Jason Wessel
2010-01-28 21:50           ` Frederic Weisbecker
2010-01-26  4:26 ` [PATCH 2/4] perf,hw_breakpoint: add lockless reservation for hw_breaks Jason Wessel
2010-01-26 19:25   ` Jason Wessel
2010-01-27 17:56     ` Frederic Weisbecker
2010-01-27 22:29       ` [PATCH 2/4] perf,hw_breakpoint: add lockless reservation forhw_breaks Jason Wessel
2010-01-26  4:26 ` [PATCH 3/4] kgdb,clocksource: Prevent kernel hang in kernel debugger Jason Wessel
2010-01-26  4:37   ` Andrew Morton
2010-01-26  8:22   ` Martin Schwidefsky
2010-01-26  8:50     ` Thomas Gleixner
2010-01-26 10:01       ` Dongdong Deng
2010-01-26 10:19         ` Xiaotian Feng
2010-01-26 10:37         ` Thomas Gleixner
2010-01-26 11:16           ` Thomas Gleixner [this message]
2010-01-26  8:45   ` Thomas Gleixner
2010-01-26 10:43   ` Thomas Gleixner
2010-01-26 14:09   ` [tip:timers/urgent] clocksource: Prevent potential kgdb dead lock tip-bot for Thomas Gleixner
2010-01-26 20:14     ` Andrew Morton
2010-01-26 20:46       ` Jason Wessel
2010-01-26  4:26 ` [PATCH 4/4] softlockup: add sched_clock_tick() to avoid kernel warning on kgdb resume Jason Wessel

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