Messages in this thread | | | Subject | Re: [PATCH v4] kmemleak: survive in a low-memory situation | From | Pekka Enberg <> | Date | Thu, 28 Mar 2019 13:50:29 +0200 |
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Hi Catalin,
On 27/03/2019 2.59, Qian Cai wrote: >>> Unless there is a brave soul to reimplement the kmemleak to embed it's >>> metadata into the tracked memory itself in a foreseeable future, this >>> provides a good balance between enabling kmemleak in a low-memory >>> situation and not introducing too much hackiness into the existing >>> code for now.
On Thu, Mar 28, 2019 at 08:05:31AM +0200, Pekka Enberg wrote: >> Unfortunately I am not that brave soul, but I'm wondering what the >> complication here is? It shouldn't be too hard to teach calculate_sizes() in >> SLUB about a new SLAB_KMEMLEAK flag that reserves spaces for the metadata.
On 28/03/2019 12.30, Catalin Marinas wrote:> I don't think it's the calculate_sizes() that's the hard part. The way > kmemleak is designed assumes that the metadata has a longer lifespan > than the slab object it is tracking (and refcounted via > get_object/put_object()). We'd have to replace some of the > rcu_read_(un)lock() regions with a full kmemleak_lock together with a > few more tweaks to allow the release of kmemleak_lock during memory > scanning (which can take minutes; so it needs to be safe w.r.t. metadata > freeing, currently relying on a deferred RCU freeing).
Right.
I think SLUB already supports delaying object freeing because of KASAN (see the slab_free_freelist_hook() function) so the issue with metadata outliving object is solvable (although will consume more memory).
I can't say I remember enough details from kmemleak to comment on the locking complications you point out, though.
- Pekka
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