linux-kernel - Re: [PATCH 02/16] hv_balloon: Replace spin_is

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Date:   Wed, 03 Oct 2018 15:20:40 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Lance Roy <ldr709@...il.com>, linux-kernel@...r.kernel.org
Cc:     "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Lance Roy <ldr709@...il.com>, devel@...uxdriverproject.org
Subject: Re: [PATCH 02/16] hv_balloon: Replace spin_is_locked() with lockdep

Lance Roy <ldr709@...il.com> writes:

> lockdep_assert_held() is better suited to checking locking requirements,
> since it won't get confused when someone else holds the lock. This is
> also a step towards possibly removing spin_is_locked().
>
> Signed-off-by: Lance Roy <ldr709@...il.com>
> Cc: "K. Y. Srinivasan" <kys@...rosoft.com>
> Cc: Haiyang Zhang <haiyangz@...rosoft.com>
> Cc: Stephen Hemminger <sthemmin@...rosoft.com>
> Cc: <devel@...uxdriverproject.org>
> ---
>  drivers/hv/hv_balloon.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> index b1b788082793..41631512ae97 100644
> --- a/drivers/hv/hv_balloon.c
> +++ b/drivers/hv/hv_balloon.c
> @@ -689,7 +689,7 @@ static void hv_page_online_one(struct hv_hotadd_state *has, struct page *pg)
>  	__online_page_increment_counters(pg);
>  	__online_page_free(pg);
>  
> -	WARN_ON_ONCE(!spin_is_locked(&dm_device.ha_lock));
> +	lockdep_assert_held(&dm_device.ha_lock);
>  	dm_device.num_pages_onlined++;
>  }

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

However,

lockdep_assert_held() is a no-op when !CONFIG_LOCKDEP but this doesn't
really matter: hv_page_online_one() is static and it has only two call
sites, both taking the dm_device.ha_lock lock - so the warning may just
go away.

-- 
Vitaly