On 2022-10-21 05:56, Yang Yingliang wrote: > > On 2022/10/21 17:08, Luben Tuikov wrote: >> 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%7C2597f1097c204be54c7c08dab34a8654%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638019429914730071%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=NNVCtbTxI5uzxxJA9mKvnsy8d3jyudtl1u4CTcm3tsU%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%7C2597f1097c204be54c7c08dab34a8654%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638019429914886316%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=ByCQk0qGktyyoNQg8IFj5AGxmaeWOXnbIA4rFnX%2B6%2BA%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(). > The name memory is allocated in kobject_set_name() in caller, and I > think caller > free the memory that it allocated is reasonable, it's weird that some > callers allocate > some memory and use function (kset_register) failed, then it free the > memory allocated > in callers, I think use kset_put()/kfree_const(name) in caller seems > more reasonable. kset_put() would work only in implementations, such as amdgpu_discovery.c, where the ktype.release is defined and it frees the embedding object in which the kset is embedded. Depending on the implementation, you may need to call kfree_const(name). And this is why this needs to be documented in kset_register(), as I noted in the review earlier. Regards, Luben
