linux-kernel - Re: [PATCH] lightnvm: pblk: avoid ref warning on cache creation

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Message-ID: <a0bacf2c-1405-b70b-828a-f2bbe0ecb271@lightnvm.io>
Date:   Fri, 30 Nov 2018 09:36:22 +0100
From:   Matias Bjørling <mb@...htnvm.io>
To:     Hans Holmberg <hans.ml.holmberg@...tronix.com>,
        Javier González <javier@...igon.com>
Cc:     Hans Holmberg <hans.holmberg@...xlabs.com>,
        linux-block@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Javier Gonzalez <javier@...xlabs.com>
Subject: Re: [PATCH] lightnvm: pblk: avoid ref warning on cache creation

On 11/23/2018 11:04 AM, Hans Holmberg wrote:
> Great catch Javier! Nice refactoring work too.
> 
> Reviewed-by: Hans Holmberg <hans.holmberg@...xlabs.com>
> On Thu, Nov 22, 2018 at 2:47 PM Javier González <javier@...igon.com> wrote:
>>
>> The current kref implementation around pblk global caches triggers a
>> false positive on refcount_inc_checked() (when called) as the kref is
>> initialized to 0. Instead of usint kref_inc() on a 0 reference, which is
>> in principle correct, use kref_init() to avoid the check. This is also
>> more explicit about what actually happens on cache creation.
>>
>> In the process, do a small refactoring to use kref helpers.
>>
>> Signed-off-by: Javier González <javier@...xlabs.com>
>> ---
>>   drivers/lightnvm/pblk-init.c | 14 +++++---------
>>   1 file changed, 5 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/lightnvm/pblk-init.c b/drivers/lightnvm/pblk-init.c
>> index 13822594647c..e225bd60cbb4 100644
>> --- a/drivers/lightnvm/pblk-init.c
>> +++ b/drivers/lightnvm/pblk-init.c
>> @@ -350,23 +350,19 @@ static int pblk_create_global_caches(void)
>>
>>   static int pblk_get_global_caches(void)
>>   {
>> -       int ret;
>> +       int ret = 0;
>>
>>          mutex_lock(&pblk_caches.mutex);
>>
>> -       if (kref_read(&pblk_caches.kref) > 0) {
>> -               kref_get(&pblk_caches.kref);
>> -               mutex_unlock(&pblk_caches.mutex);
>> -               return 0;
>> -       }
>> +       if (kref_get_unless_zero(&pblk_caches.kref))
>> +               goto out;
>>
>>          ret = pblk_create_global_caches();
>> -
>>          if (!ret)
>> -               kref_get(&pblk_caches.kref);
>> +               kref_init(&pblk_caches.kref);
>>
>> +out:
>>          mutex_unlock(&pblk_caches.mutex);
>> -
>>          return ret;
>>   }
>>
>> --
>> 2.7.4
>>

Picked up for 4.21.