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Date:   Mon, 27 Jul 2020 16:36:55 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Joerg Vehlow <lkml@jv-coder.de>
Cc:     Steven Rostedt <rostedt@goodmis.org>, linux-kernel@vger.kernel.org,
        Joerg Vehlow <joerg.vehlow@aox-tech.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Huang Ying <ying.huang@intel.com>
Subject: Re: [BUG RT] dump-capture kernel not executed for panic in
 interrupt context
Message-Id: <20200727163655.8c94c8e245637b62311f5053@linux-foundation.org>
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On Wed, 22 Jul 2020 06:30:53 +0200 Joerg Vehlow <lkml@jv-coder.de> wrote:

> >> About 12 years ago this was not implemented using a mutex, but using xchg.
> >> See: 8c5a1cf0ad3ac5fcdf51314a63b16a440870f6a2
> > Yes, that commit is wrong, because mutex_trylock() is not to be taken in
> > interrupt context, where crash_kexec() looks like it can be called.

Yup, mutex_trylock() from interrupt is improper.  Well dang, that's a
bit silly.  Presumably the 2006 spin_lock_mutex() wasn't taken with
irqs-off.

Ho hum, did you look at switching the kexec code back to the xchg
approach?