On 2022-10-21 04:36, 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%7Ca8206f9348e04b13e3da08dab33f4f53%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638019381738406942%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=HqvF1p4ejF6%2BYS5u0pe15ZdDgUAIVP%2BB1xQXICWjNwY%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%7Ca8206f9348e04b13e3da08dab33f4f53%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638019381738406942%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=LmRgWUSQgK6wJvMdfBgjO4CiaKQ2TBoeW836r0UbcjU%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. WLOG, I believe it is something like this: x = kzalloc(); kobject_set_name(&x->kset.kobj, format, ...); x->kset.kobj.kset = parent_kset; x->kset.kobj.ktype = this_ktype; /* this has a .release which frees x */ res = kset_register(&x->kset); if (res) { kset_put(&x->kset); /* calls this_ktype->release() which frees x */ kfree(x); /* <-- double free */ } And since kref is set to 1, in kset_register(), then we'd double free. This is why I don't have kset_put() in that error path in amdgpu. Regards, Luben
