linux-kernel - [PATCH v3 0/3] mm/slub: some debug enhancements

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Date:   Wed, 27 Jul 2022 15:10:39 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Robin Murphy <robin.murphy@....com>,
        John Garry <john.garry@...wei.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Feng Tang <feng.tang@...el.com>
Subject: [PATCH v3 0/3] mm/slub: some debug enhancements 

kmalloc's API family is critical for mm, and one of its nature is that
it will round up the request size to a fixed one (mostly power of 2).
When user requests memory for '2^n + 1' bytes, actually 2^(n+1) bytes
could be allocated, so in worst case, there is around 50% memory space
waste.

The wastage is not a big issue for requests that get allocated/freed 
quickly, but may cause problems with objects that have longer life time,
and there were some OOM cases in some extrem cases.

This patchset tries to :
* Add a debug method to track each kmalloced object's wastage info,
  and show the call stack of original allocation
* Extend the redzone sanity check to the extra kmalloced buffer than
  requested, to better detect un-legitimate access to it.

Please help to review, thanks!

- Feng

---
Changelogs:

  since v2:
    * rebased against slab tree's 'for-next' branch
    * fix pointer handling (Kefeng Wang)
    * move kzalloc zeroing handling change to a separate patch (Vlastimil Babka) 
    * make 'orig_size' only depend on KMALLOC & STORE_USER flag
      bits (Vlastimil Babka)

  since v1:
    * limit the 'orig_size' to kmalloc objects only, and save
      it after track in metadata (Vlastimil Babka)
    * fix a offset calculation problem in print_trailer

  since RFC:
    * fix problems in kmem_cache_alloc_bulk() and records sorting,
      improve the print format (Hyeonggon Yoo)
    * fix a compiling issue found by 0Day bot
    * update the commit log based info from iova developers


Feng Tang (3):
  mm/slub: enable debugging memory wasting of kmalloc
  mm/slub: only zero the requested size of buffer for kzalloc
  mm/slub: extend redzone check to cover extra allocated kmalloc space
    than requested

 include/linux/slab.h |   2 +
 mm/slab.c            |   8 +--
 mm/slab.h            |   9 ++-
 mm/slub.c            | 157 ++++++++++++++++++++++++++++++++++++-------
 4 files changed, 146 insertions(+), 30 deletions(-)

-- 
2.27.0