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

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Date:	Wed, 25 Nov 2015 16:57:25 +0800
From:	Wenwei Tao <ww.tao0320@...il.com>
To:	Matias <mb@...htnvm.io>
Cc:	linux-kernel@...r.kernel.org, linux-block@...r.kernel.org
Subject: Re: [PATCH] lightnvm: missing nvm_lock acquire

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@...htnvm.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@...il.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?
--
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