linux-kernel - Re: [PATCH RT 1/2 v2] dm-snapshot: fix crash with the realtime kernel

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Message-ID: <20191125172512.q65pmda66un3cm2e@linutronix.de>
Date:   Mon, 25 Nov 2019 18:25:12 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Mikulas Patocka <mpatocka@...hat.com>
Cc:     Mike Snitzer <msnitzer@...hat.com>,
        Nikos Tsironis <ntsironis@...ikto.com>,
        Scott Wood <swood@...hat.com>,
        Ilias Tsitsimpis <iliastsi@...ikto.com>, dm-devel@...hat.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Daniel Wagner <dwagner@...e.de>,
        linux-rt-users@...r.kernel.org, tglx@...utronix.de
Subject: Re: [PATCH RT 1/2 v2] dm-snapshot: fix crash with the realtime kernel

On 2019-11-12 11:09:51 [-0500], Mikulas Patocka wrote:
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-snap.c	2019-11-12 16:44:36.000000000 +0100
> +++ linux-2.6/drivers/md/dm-snap.c	2019-11-12 17:01:46.000000000 +0100
…
>  static void dm_exception_table_lock(struct dm_exception_table_lock *lock)
>  {
> +#ifndef CONFIG_PREEMPT_RT_BASE
>  	hlist_bl_lock(lock->complete_slot);
>  	hlist_bl_lock(lock->pending_slot);
> +#else
> +	spin_lock(lock->lock);

if you also set the lowest bit for complete_slot + pending_slot then
patch 2 of this mini series wouldn't be required. That means we could
keep the debug code on -RT. Or am I missing something?

> +#endif
>  }

Sebastian