Messages in this thread | | | Date | Mon, 12 Jun 2006 23:24:37 +0100 | From | "Catalin Marinas" <> | Subject | Re: [PATCH 2.6.17-rc6 7/9] Remove some of the kmemleak false positives |
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On 12/06/06, Ingo Molnar <mingo@elte.hu> wrote: > > * Catalin Marinas <catalin.marinas@gmail.com> wrote: > > > On 12/06/06, Ingo Molnar <mingo@elte.hu> wrote: > > >What i'd like to see though are clear explanations about why an > > >allocation is not considered a leak, in terms of comments added to the > > >code. That will also help us reduce the number of annotations later on. > > > > I'll document them in both Documentation/kmemleak.txt and inside the > > code. If I implement the "any pointer inside the block" method, all > > the memleak_padding() false positives will disappear. > > i dont know - i feel uneasy about the 'any pointer' method - it has a > high potential for false negatives, especially for structures that > contain strings (or other random data), etc.
That's my concern as well. The advantage is that it simplifies kmemleak but I can't tell how good the detection would be. I can add some code to the current implementation to show how many values (32 bit aligned) found during scanning look like valid pointers (i.e. PAGE_OFFSET < x < PAGE_OFFSET + ram_size) but cannot be found in the radix_tree. It might not be that bad (I'll post tomorrow some statistics).
> did you consider the tracking of the types of allocated blocks > explicitly? I'd expect that most blocks dont have pointers embedded in > them that point to allocated blocks. For the ones that do, the > allocation could be extended with the type information. For each > affected type, we could annotate the structures themselves with offset > information. How intrusive would such a method be?
Do you mean that when scanning it should only consider at the pointer members in a structure? I don't think this can be easily achieved because of the amount of structures in the kernel. There are places where a pointer is stored as a long. There is also no way in C to quantify the type of an object (similar to "typeid" in C++). The closest approximation I could get was the size.
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