linux-kernel - Re: [PATCH 5/8] dax: refactor locking out of size calculation routines

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Date:   Wed, 14 Dec 2016 07:55:31 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Johannes Thumshirn <jthumshirn@...e.de>
Cc:     "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/8] dax: refactor locking out of size calculation routines

On Wed, Dec 14, 2016 at 7:01 AM, Johannes Thumshirn <jthumshirn@...e.de> wrote:
> Hi Dan,
>
> On Sat, Dec 10, 2016 at 10:28:51PM -0800, Dan Williams wrote:
>> In preparation for other callers of these routines make the locking the
>> responsibility of the caller.
>>
>> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
>> ---
>>  drivers/dax/dax.c |   30 ++++++++++++++++++++++++------
>>  1 file changed, 24 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
>> index d878a56cf3e3..5b65eaff6ace 100644
>> --- a/drivers/dax/dax.c
>> +++ b/drivers/dax/dax.c
>> @@ -90,11 +90,11 @@ static unsigned long long dax_region_avail_size(
>>       unsigned long long size;
>>       struct resource *res;
>>
>> -     mutex_lock(&dax_region->lock);
>> +     WARN_ON_ONCE(!mutex_is_locked(&dax_region->lock));
>
> I'd prefer it a lockdep_assert_held(&dex_region->lock). This of cause has the
> drawback that it won't trigger w/o lockdep but enabled, but I don't think it's
> the responibility of a production kernel to have this warnings anyway. On the
> flip side you get all the lockdep beauty for free with it.

True, yes, it's only a developer debug warning. I'll change it and fix
up the other pattern like this in libnvdimm.