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Date:   Mon, 7 Nov 2022 17:30:16 +0100
From:   Jan Kara <jack@suse.cz>
To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     Jan Kara <jack@suse.cz>, LKML <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mel Gorman <mgorman@suse.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        Waiman Long <longman@redhat.com>,
        Catalin Marinas <catalin.marinas@arm.com>
Subject: Re: Crash with PREEMPT_RT on aarch64 machine
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On Mon 07-11-22 16:10:34, Sebastian Andrzej Siewior wrote:
> + locking, arm64
> 
> On 2022-11-07 14:56:36 [+0100], Jan Kara wrote:
> > > spinlock_t and raw_spinlock_t differ slightly in terms of locking.
> > > rt_spin_lock() has the fast path via try_cmpxchg_acquire(). If you
> > > enable CONFIG_DEBUG_RT_MUTEXES then you would force the slow path which
> > > always acquires the rt_mutex_base::wait_lock (which is a raw_spinlock_t)
> > > while the actual lock is modified via cmpxchg. 
> > 
> > So I've tried enabling CONFIG_DEBUG_RT_MUTEXES and indeed the corruption
> > stops happening as well. So do you suspect some bug in the CPU itself?
> 
> If it is only enabling CONFIG_DEBUG_RT_MUTEXES (and not whole lockdep)
> then it looks very suspicious. 

Just to confirm, CONFIG_DEBUG_RT_MUTEXES is the only thing I've enabled and
the list corruption disappeared.

								Honza

-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR