Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Sat, 22 Aug 2020 14:32:52 +0200
From:   peterz@infradead.org
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Joerg Vehlow <lkml@jv-coder.de>,
        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>, dave@stgolabs.net
Subject: Re: [BUG RT] dump-capture kernel not executed for panic in interrupt
 context
Message-ID: <20200822123252.GQ1362448@hirez.programming.kicks-ass.net>
References: <2c243f59-6d10-7abb-bab4-e7b1796cd54f@jv-coder.de>
 <20200528084614.0c949e8d@gandalf.local.home>
 <cbbf7926-148e-7acb-dc03-3f055d73364b@jv-coder.de>
 <20200727163655.8c94c8e245637b62311f5053@linux-foundation.org>
 <c6b095af-fc92-420f-303f-d2efd9f28873@jv-coder.de>
 <20200821110848.6c3183d1@oasis.local.home>
 <20200821134753.9547695c9b782275be3c95b5@linux-foundation.org>
 <20200821170334.73b52fdd@oasis.local.home>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200821170334.73b52fdd@oasis.local.home>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Aug 21, 2020 at 05:03:34PM -0400, Steven Rostedt wrote:

> > Sigh.  Is it too hard to make mutex_trylock() usable from interrupt
> > context?
> 
> 
> That's a question for Thomas and Peter Z.

You should really know that too, the TL;DR answer is it's fundamentally
buggered, can't work.

The problem is that RT relies on being able to PI boost the mutex owner.

ISTR we had a thread about all this last year or so, let me see if I can
find that.

Here goes:

  https://lkml.kernel.org/r/20191218135047.GS2844@hirez.programming.kicks-ass.net

Kexec even gets mentioned:

  https://lkml.kernel.org/r/20191219090535.GV2844@hirez.programming.kicks-ass.net