Hi,
On 5/25/23 21:50, Mark Pearson wrote:
>
>
> On Thu, May 25, 2023, at 3:41 PM, Hans de Goede wrote:
>> Hi Mark,
>>
>> On 5/25/23 21:31, Mark Pearson wrote:
>>> Add mutex protection around cases where an operation needs multiple
>>> WMI calls - e.g. setting password.
>>>
>>> Signed-off-by: Mark Pearson <mpearson-lenovo@xxxxxxxxx>
>>> ---
>>> Changes in V2: New commit added after review of other patches in series.
>>>
>>> drivers/platform/x86/think-lmi.c | 46 ++++++++++++++++++++++++--------
>>> 1 file changed, 35 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/drivers/platform/x86/think-lmi.c b/drivers/platform/x86/think-lmi.c
>>> index 64cd453d6e7d..f3e1e4dacba2 100644
>>> --- a/drivers/platform/x86/think-lmi.c
>>> +++ b/drivers/platform/x86/think-lmi.c
>>> @@ -14,6 +14,7 @@
>>> #include <linux/acpi.h>
>>> #include <linux/errno.h>
>>> #include <linux/fs.h>
>>> +#include <linux/mutex.h>
>>> #include <linux/string.h>
>>> #include <linux/types.h>
>>> #include <linux/dmi.h>
>>> @@ -195,6 +196,7 @@ static const char * const level_options[] = {
>>> };
>>> static struct think_lmi tlmi_priv;
>>> static struct class *fw_attr_class;
>>> +static DEFINE_MUTEX(tlmi_mutex);
>>>
>>> /* ------ Utility functions ------------*/
>>> /* Strip out CR if one is present */
>>> @@ -463,23 +465,32 @@ static ssize_t new_password_store(struct kobject *kobj,
>>> sprintf(pwd_type, "%s", setting->pwd_type);
>>> }
>>>
>>> + mutex_lock(&tlmi_mutex);
>>> ret = tlmi_opcode_setting("WmiOpcodePasswordType", pwd_type);
>>> - if (ret)
>>> + if (ret) {
>>> + mutex_unlock(&tlmi_mutex);
>>> goto out;
>>> -
>>> + }
>>> if (tlmi_priv.pwd_admin->valid) {
>>> ret = tlmi_opcode_setting("WmiOpcodePasswordAdmin",
>>> tlmi_priv.pwd_admin->password);
>>> - if (ret)
>>> + if (ret) {
>>> + mutex_unlock(&tlmi_mutex);
>>> goto out;
>>> + }
>>> }
>>> ret = tlmi_opcode_setting("WmiOpcodePasswordCurrent01", setting->password);
>>> - if (ret)
>>> + if (ret) {
>>> + mutex_unlock(&tlmi_mutex);
>>> goto out;
>>> + }
>>> ret = tlmi_opcode_setting("WmiOpcodePasswordNew01", new_pwd);
>>> - if (ret)
>>> + if (ret) {
>>> + mutex_unlock(&tlmi_mutex);
>>> goto out;
>>> + }
>>> ret = tlmi_simple_call(LENOVO_OPCODE_IF_GUID, "WmiOpcodePasswordSetUpdate;");
>>> + mutex_unlock(&tlmi_mutex);
>>> } else {
>>> /* Format: 'PasswordType,CurrentPw,NewPw,Encoding,KbdLang;' */
>>> auth_str = kasprintf(GFP_KERNEL, "%s,%s,%s,%s,%s;",
>>
>>
>> I haven't take a really close / good look yet. But at a first glance
>> I think it would be cleaner to just take the mutex at the top
>> and unlock it after the out label to which all the existing goto-s
>> already go ?
>>
> I did consider that - and it was in my first implementation; but then I got concerned
> about if the mutex_unlock could potentially get called without mutex_lock having been
> called beforehand. I couldn't find any good reference as to whether that was safe or not.
>
> I ended up deciding that a few extra brackets and unlock calls wasn't that ugly and was 'safer'...and
> so went that route.
>
> Happy to change it - but do you happen to know if it's safe to call unlock without a lock? If it is then
> that implementation is cleaner.
It is not allowed to unlock without a lock. But if you put the lock directly after the malloc for which the out: does the free then there should be no goto out paths which don't have the lock.
E.g. for new_password_store() put it here:
new_pwd = kstrdup(buf, GFP_KERNEL);
if (!new_pwd)
return -ENOMEM;
mutex_lock(&tlmi_mutex);
/* Strip out CR if one is present, setting password won't work if it is present */
...
This does mean also taking the lock in the case where the new password store is done with a single WMI call, but that is not an issue. It makes things a tiny bit slower but WMI calls already are not fast and it is not like we are going to change the password / settings 100-times per second.
And the same thing can be done in current_value_store():
new_setting = kstrdup(buf, GFP_KERNEL);
if (!new_setting)
return -ENOMEM;
mutex_lock(&tlmi_mutex);
/* Strip out CR if one is present */
...
Regards,
Hans
