Re: [PATCH] lightnvm: missing nvm_lock acquire

Wenwei Tao
2015-11-25T14:18:48Z

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@gmail.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@lightnvm.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@gmail.com>
>> Signed-off-by: Matias Bjørling <m@bjorling.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
>>
>>