linux-kernel - Re: [PATCH] lightnvm: missing nvm

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Date:	Wed, 25 Nov 2015 22:18:45 +0800
From:	Wenwei Tao <ww.tao0320@...il.com>
To:	Matias Bjørling <mb@...htnvm.io>
Cc:	linux-kernel@...r.kernel.org, linux-block@...r.kernel.org
Subject: Re: [PATCH] lightnvm: missing nvm_lock acquire

Or we can add a new function

static struct nvm_dev *nvm_find_nvm_dev_locked(const char *name)
 {
        struct nvm_dev *dev;

+       down_write(&nvm_lock);
        list_for_each_entry(dev, &nvm_devices, devices)
                if (!strcmp(name, dev->name))
                        return dev;
+       up_write(&nvm_lock);

        return NULL;
 }

use nvm_find_nvm_dev_locked() and nvm_find_nvm_dev() properly.

2015-11-25 21:11 GMT+08:00 Wenwei Tao <ww.tao0320@...il.com>:
> Hi Matias
>
> Place the lock inside nvm_find_nvm_dev can make code cleaner, but
> sometime may lack of flexibility, cause redundant lock and unlock,
> just my opinion. Place the lock inside the function is okay with me,
> just make sure do the proper up_write(&nvm_lock) in
> nvm_create_target(), it has a lot 'return'.
>
> I just submit a patch set covering the lock issue and the target issue
> mentioned before, you can have a look before you apply this patch.
> Thanks.
>
> 2015-11-25 19:37 GMT+08:00 Matias Bjørling <mb@...htnvm.io>:
>> On 11/25/2015 09:57 AM, Wenwei Tao wrote:
>>>
>>> Hi Matias
>>> I think list_for_each_entry_safe(pos, n, head, member) cannot avoid
>>> race condition
>>> the item point by ‘n’ can be deleted and freed in the same time we
>>> operate on 'pos'
>>> so lock is still necessary.
>>>
>> I've made the patch like this, ok?
>>
>> To avoid race conditions, traverse dev, media manager,
>> and target lists and also register, unregister entries
>> to/from them, should be always under the nvm_lock control.
>>
>> Signed-off-by: Wenwei Tao <ww.tao0320@...il.com>
>> Signed-off-by: Matias Bjørling <m@...rling.me>
>> ---
>>  drivers/lightnvm/core.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/lightnvm/core.c b/drivers/lightnvm/core.c
>> index ea6dba5..9f901f6 100644
>> --- a/drivers/lightnvm/core.c
>> +++ b/drivers/lightnvm/core.c
>> @@ -127,9 +127,11 @@ static struct nvm_dev *nvm_find_nvm_dev(const char
>> *name)
>>  {
>>         struct nvm_dev *dev;
>>
>> +       down_write(&nvm_lock);
>>         list_for_each_entry(dev, &nvm_devices, devices)
>>                 if (!strcmp(name, dev->name))
>>                         return dev;
>> +       up_write(&nvm_lock);
>>
>>         return NULL;
>>  }
>> @@ -388,13 +390,14 @@ static int nvm_create_target(struct nvm_dev *dev,
>>                 }
>>         }
>>
>> +       down_write(&nvm_lock);
>>
>>         tt = nvm_find_target_type(create->tgttype);
>>         if (!tt) {
>>                 pr_err("nvm: target type %s not found\n", create->tgttype);
>> +               up_write(&nvm_lock);
>>                 return -EINVAL;
>>         }
>>
>> -       down_write(&nvm_lock);
>>         list_for_each_entry(t, &dev->online_targets, list) {
>>                 if (!strcmp(create->tgtname, t->disk->disk_name)) {
>>                         pr_err("nvm: target name already exists.\n");
>> --
>> 2.1.4
>>
>>
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