On 2022-10-21 04:24, Luben Tuikov wrote: > On 2022-10-21 04:18, Greg KH wrote: >> On Fri, Oct 21, 2022 at 03:55:18AM -0400, Luben Tuikov wrote: >>> On 2022-10-21 01:37, 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%7Cd41da3fd6449492d01f808dab33cdb75%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638019371236833115%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=C%2Bj1THkHpzVGks5eqB%2Fm%2FPAkMRohR7CYvRnOCqUqdcM%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%7Cd41da3fd6449492d01f808dab33cdb75%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638019371236833115%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=pSR10abmK8nAMvKSezqWC0SPUBL4qEwtCCizyIKW7Dc%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. >>> >>> Looking at kset_register(), we can add kset_put() in the error path, >>> when kobject_add_internal(&kset->kobj) fails. >>> >>> See the attached patch. It needs to be tested with the same error injection >>> as Yang has been doing. >>> >>> Now, struct kset is being embedded in larger structs--see amdgpu_discovery.c >>> starting at line 575. If you're on an AMD system, it gets you the tree >>> structure you'll see when you run "tree /sys/class/drm/card0/device/ip_discovery/". >>> That shouldn't be a problem though. >> >> Yes, that shouldn't be an issue as the kobject embedded in a kset is >> ONLY for that kset itself, the kset structure should not be controling >> the lifespan of the object it is embedded in, right? > > Yes, and it doesn't. It only does a kobject_get(parent) and kobject_put(parent). > So that's fine and natural. > > Yang, do you want to try the patch in my previous email in this thread, since you've > got the error injection set up already? I spoke too soon. I believe you're onto something, because looking at the idiom: kobj_set_name(&kset->kobj, format, ...); kset->kobj.kset = parent_kset; kset->kobj.ktype = ktype; res = kset_register(kset); The ktype defines a release method, which frees the larger struct the kset is embedded in. And this would result in double free, for instance in the amdgpu_discovery.c code, if kset_put() is called after kset_register() fails, since we kzalloc the larger object just before and kfree it on error just after. Ideally, we'd only "revert" the actions done by kobj_set_name(), as there's some error recovery on create_dir() in kobject_add_internal(). So, we cannot do this business with the kset_put() on error from kset_register(), after all. Not sure how this wasn't caught in Yang's testing--the kernel should've complained. Regards, Luben
