Re: [PATCH] lightnvm: missing nvm_lock acquire

Wenwei Tao
2015-11-25T08:57:28Z

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.

2015-11-25 2:36 GMT+08:00 Matias <mb@lightnvm.io>:
> On 11/24/2015 04:24 PM, Wenwei Tao wrote:
>>
>> To avoid race conditions, traverse dev, media manager,
>> and targeet 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>
>> ---
>> drivers/lightnvm/core.c | 19 +++++++++++++------
>> 1 file changed, 13 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/lightnvm/core.c b/drivers/lightnvm/core.c
>> index f659e60..39aec3a 100644
>> --- a/drivers/lightnvm/core.c
>> +++ b/drivers/lightnvm/core.c
>> @@ -333,19 +333,19 @@ EXPORT_SYMBOL(nvm_register);
>>
>> void nvm_unregister(char *disk_name)
>> {
>> + down_write(&nvm_lock);
>> struct nvm_dev *dev = nvm_find_nvm_dev(disk_name);
>
>
> In nvm_find_nvm_dev, can we instead replace it with
> list_for_each_entry_safe. Then we are sure that we won't hit a missing
> element, and will make the other cases significantly cleaner.
>
>>
>> if (!dev) {
>> pr_err("nvm: could not find device %s to unregister\n",
>>
>> disk_name);
>> + up_write(&nvm_lock);
>> return;
>> }
>>
>> - nvm_exit(dev);
>> -
>> - down_write(&nvm_lock);
>> list_del(&dev->devices);
>> up_write(&nvm_lock);
>> + nvm_exit(dev);
>> }
>> EXPORT_SYMBOL(nvm_unregister);
>>
>> @@ -365,12 +365,15 @@ static int nvm_create_target(struct nvm_dev *dev,
>> void *targetdata;
>> int ret = 0;
>>
>> + down_write(&nvm_lock);
>> if (!dev->mt) {
>> /* register with device with a supported NVM manager */
>> list_for_each_entry(mt, &nvm_mgrs, list) {
>
>
> Same with this one?