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From: peterz@infradead.org
To: Joerg Vehlow <lkml@jv-coder.de>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Huang Ying <ying.huang@intel.com>,
	linux-kernel@vger.kernel.org,
	Joerg Vehlow <joerg.vehlow@aox-tech.de>
Subject: Re: [BUG RT] dump-capture kernel not executed for panic in interrupt context
Date: Mon, 7 Sep 2020 18:23:38 +0200	[thread overview]
Message-ID: <20200907162338.GN1362448@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <5c3a502f-2255-5aae-3599-5220aa4b8328@jv-coder.de>

On Mon, Sep 07, 2020 at 02:03:09PM +0200, Joerg Vehlow wrote:
> 
> 
> On 9/7/2020 1:46 PM, peterz@infradead.org wrote:
> > I think it's too complicated for that is needed, did you see my
> > suggestion from a year ago? Did i miss something obvious?
> > 
> This one? https://lore.kernel.org/linux-fsdevel/20191219090535.GV2844@hirez.programming.kicks-ass.net/
> 
> I think it may be a bit incorrect?
> According to the original comment in __crash_kexec, the mutex was used to
> prevent a sys_kexec_load, while crash_kexec is executed. Your proposed patch
> does not lock the mutex in crash_kexec.

Sure, but any mutex taker will (spin) wait for panic_cpu==CPU_INVALID.
And if the mutex is already held, we'll not run __crash_kexec() just
like the trylock() would do today.

> This does not cover the original use
> case anymore. The only thing that is protected now are two panicing cores at
> the same time.

I'm not following. AFAICT it does exactly what the old code did.
Although maybe I didn't replace all kexec_mutex users, I now see that
thing isn't static.

> Actually, this implementation feels even more hacky to me....

It's more minimal ;-) It's simpler in that it only provides the required
semantics (as I understand them) and does not attempt to implement a
more general trylock() like primitive that isn't needed.

Also, read the kexec_lock() implementation you posted and explain to me
what happens when kexec_busy is elevated. Also note the lack of
confusing loops in my code.

  reply	other threads:[~2020-09-07 16:24 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-28 11:41 [BUG RT] dump-capture kernel not executed for panic in interrupt context Joerg Vehlow
2020-05-28 12:46 ` Steven Rostedt
2020-07-22  4:30   ` Joerg Vehlow
2020-07-22 20:51     ` Steven Rostedt
2020-07-27 23:36     ` Andrew Morton
2020-08-21 10:25       ` Joerg Vehlow
2020-08-21 15:08         ` Steven Rostedt
2020-08-21 20:47           ` Andrew Morton
2020-08-21 21:03             ` Steven Rostedt
2020-08-22 12:32               ` peterz
2020-08-22 23:49                 ` Steven Rostedt
2020-09-07 11:41                   ` peterz
2020-09-07 12:49                     ` Valentin Schneider
2020-09-14 19:00                     ` Steven Rostedt
2020-09-07 10:51               ` Joerg Vehlow
2020-09-07 11:46                 ` peterz
2020-09-07 12:03                   ` Joerg Vehlow
2020-09-07 16:23                     ` peterz [this message]
2020-09-08  5:48                       ` Joerg Vehlow
2020-09-09  5:46                         ` Joerg Vehlow
2020-09-11 22:48                           ` Eric W. Biederman
2020-09-14  6:03                             ` Joerg Vehlow
2020-09-14 16:46                               ` Eric W. Biederman

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