Messages in this thread | | | Date | Fri, 7 Dec 2012 00:02:11 +0100 | Subject | Re: [PATCH v2 1/1] uio.c: solve memory leak | From | Cong Ding <> |
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ping Hans, did you have any comment on this?
- cong
On Fri, Nov 30, 2012 at 12:03 PM, Cong Ding <dinggnu@gmail.com> wrote: > Hi Hans, I think the memory allocated with kzalloc is properly freed > by calling kobject_put. > > I can give a simple explanation. > > 1) when we call kobject_init, the parameter portio_attr_type is > passed in. portio_attr_type includes a function pointer to > portio_release, which releases the memory of portio. > > 2) when we call kobject_put, kref_put is called with the pointer of > function kobject_release. > 3) kref_put calls kref_sub, with the same pointer of function kobject_release. > 4) and kref_put calls the function kboject_release if > atomic_sub_and_test returns true > > 5) let's look at what kobject_release is. it calls kobject_cleanup, > and kobject_cleanup calls t->release(kobj) where t->release is exactly > the function we passed in through portio_init at step (1). so function > portio_release is called, and the memory allocated with kzalloc is > freed. > > If there are anything wrong in my analysis, please feel free to let me know. > > Personally, I suggest to add a function to create and release > uio_portio, which is similar as kobject_create and kobject_put in file > lib/kobject.c. In this way, it avoid other readers thinking the memory > is not freed (and we should add some comments here). For example, > uio_portio_create call kzalloc and kboject_init, and returns > uio_portio, which is similar as function kobject_create; and > uio_portio_release calls kobject_put to release the memory. And we do > same thing for uio_map. > > The usage here is quite strange, but it works. If I write this > function from zero, I will use a pointer to kobject in uio_portio > struct instead of kobject struct itself. In this case I can call > kobject_create instead of kobject_init, and then we do both > kzalloc(uio_portio) and kfree(uio_portio) in the file uio.c. > > Best, > Cong > > On Fri, Nov 30, 2012 at 1:13 AM, Hans J. Koch <hjk@hansjkoch.de> wrote: >> There's still another bug: The memory allocated with kzalloc is >> never freed.
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