Messages in this thread | | | Subject | Re: Leaks in trace reported by kmemleak | From | Catalin Marinas <> | Date | Mon, 19 Oct 2009 13:00:05 +0100 |
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On Mon, 2009-10-19 at 11:15 +0200, Zdenek Kabelac wrote: > 2009/10/16 Catalin Marinas <catalin.marinas@arm.com>: > > On Fri, 2009-10-16 at 17:07 +0200, Zdenek Kabelac wrote: > >> So I've tested this modified version and it gives much better result > >> with respect to amount of leaked objects > > > > BTW, I created this tree with kmemleak patches to be pushed upstream: > > > > git://git.kernel.org/pub/scm/linux/kernel/git/cmarinas/kmemleak.git > > > > It would be easier to test. > > Yes this branch worked well - and there were no leaks from i915 or > kvm modules for trace. > > What is however interesting is the false positive leak for > dma_debug_init(). Which is sometimes listed and sometimes not - the > memory is allocated just once in the code during boot, so it's strange > that pointers to that area are sometimes out of kmemleak scan.
I updated the tree above with another patch which lists where an object is referred from. So when you get a leak reported and it later disappears, you can use:
echo dump=0x... > /sys/kernel/debug/kmemleak
and in syslog you can find information about the previously reported object and where it is referred from (if it is no longer reported as a leak). I'm not sure whether this option would be useful for anything other than debugging kmemleak. I still aim on getting to near 0 false positives.
Anyway, trying this new patch on the debug_objects, when no longer reported they are referred from obj_hash. My opinion is that they were moved to obj_hash during the kmemleak scanning but after kmemleak finished scanning the data section, hence they couldn't be found.
I hoped that not reporting object allocated within the last 5s would avoid such problems but there are places like debug_objects for which it doesn't work as the objects were reported earlier.
A workaround I had in the past was to not report an object unless it was found as a leak in two consecutive scans. I should probably reinstate this feature (could be optimised to use a second prio_tree containing only objects found as leaks).
-- Catalin
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