[v3,0/3] mm/slub: some debug enhancements

Message

Feng Tang July 27, 2022, 7:10 a.m. UTC

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(-)