On 2022-10-21 04:59, Yang Yingliang wrote: > > On 2022/10/21 16:36, Greg KH wrote: >> On Fri, Oct 21, 2022 at 04:24:23PM +0800, Yang Yingliang wrote: >>> On 2022/10/21 13:37, Greg KH wrote: >>>> On Fri, Oct 21, 2022 at 01:29:31AM -0400, Luben Tuikov wrote: >>>>> On 2022-10-20 22:20, Yang Yingliang wrote: >>>>>> The previous discussion link: >>>>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2F0db486eb-6927-927e-3629-958f8f211194%40huawei.com%2FT%2F&data=05%7C01%7Cluben.tuikov%40amd.com%7C74aa9b57192b406ef27408dab3429db4%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638019395979868103%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=RcK05cXm1J5%2BtYcLO2SMG7k6sjeymQzdBzMCDJSzfdE%3D&reserved=0 >>>>> The very first discussion on this was here: >>>>> >>>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.spinics.net%2Flists%2Fdri-devel%2Fmsg368077.html&data=05%7C01%7Cluben.tuikov%40amd.com%7C74aa9b57192b406ef27408dab3429db4%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638019395979868103%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=sHZ6kfLF8HxrNXV6%2FVjgdH%2BmQM4T3Zv0U%2FAwddT97cE%3D&reserved=0 >>>>> >>>>> Please use this link, and not the that one up there you which quoted above, >>>>> and whose commit description is taken verbatim from the this link. >>>>> >>>>>> kset_register() is currently used in some places without calling >>>>>> kset_put() in error path, because the callers think it should be >>>>>> kset internal thing to do, but the driver core can not know what >>>>>> caller doing with that memory at times. The memory could be freed >>>>>> both in kset_put() and error path of caller, if it is called in >>>>>> kset_register(). >>>>> As I explained in the link above, the reason there's >>>>> a memory leak is that one cannot call kset_register() without >>>>> the kset->kobj.name being set--kobj_add_internal() returns -EINVAL, >>>>> in this case, i.e. kset_register() fails with -EINVAL. >>>>> >>>>> Thus, the most common usage is something like this: >>>>> >>>>> kobj_set_name(&kset->kobj, format, ...); >>>>> kset->kobj.kset = parent_kset; >>>>> kset->kobj.ktype = ktype; >>>>> res = kset_register(kset); >>>>> >>>>> So, what is being leaked, is the memory allocated in kobj_set_name(), >>>>> by the common idiom shown above. This needs to be mentioned in >>>>> the documentation, at least, in case, in the future this is absolved >>>>> in kset_register() redesign, etc. >>>> Based on this, can kset_register() just clean up from itself when an >>>> error happens? Ideally that would be the case, as the odds of a kset >>>> being embedded in a larger structure is probably slim, but we would have >>>> to search the tree to make sure. >>> I have search the whole tree, the kset used in bus_register() - patch #3, >>> kset_create_and_add() - patch #4 >>> __class_register() - patch #5, fw_cfg_build_symlink() - patch #6 and >>> amdgpu_discovery.c - patch #10 >>> is embedded in a larger structure. In these cases, we can not call >>> kset_put() in error path in kset_register() >> Yes you can as the kobject in the kset should NOT be controling the >> lifespan of those larger objects. >> >> If it is, please point out the call chain here as I don't think that >> should be possible. >> >> Note all of this is a mess because the kobject name stuff was added much >> later, after the driver model had been created and running for a while. >> We missed this error path when adding the dynamic kobject name logic, >> thank for looking into this. >> >> If you could test the patch posted with your error injection systems, >> that could make this all much simpler to solve. > > The patch posted by Luben will cause double free in some cases. Yes, I figured this out in the other email and posted the scenario Greg was asking about. But I believe the question still stands if we can do kset_put() after a *failed* kset_register(), namely if more is being done than necessary, which is just to free the memory allocated by kobject_set_name(). Regards, Luben
