[PATCH 0/2] mm/shrinker: make unregister_shrinker() less fragile

[Sergey Senozhatsky]

Hello,

Shrinker API does not handle nicely unregister_shrinker() on a not-registered
->shrinker. Looking at shrinker users, they all have to
(a) carry on some sort of a flag to make sure that "unregister_shrinker()"
will not blow up later
(b) be fishy (potentially can Oops)
(c) access private members `struct shrinker' (e.g. `shrink.list.next')

Change unregister_shrinker() to consider all-zeroes shrinker as
'initialized, but not registered' shrinker, so we can avoid NULL
dereference when unregister_shrinker() accidentally receives such
a struct.

Introduce init_shrinker() function to init `critical' shrinkers members
when the entire shrinker cannot be, for some reason, zeroed out. This
also helps to avoid Oops in unregister_shrinker() in some cases (when
unregister_shrinker() receives not initialized and not registered shrinker).

Sergey Senozhatsky (2):
  mm/shrinker: do not NULL dereference uninitialized shrinker
  mm/shrinker: add init_shrinker() function

 include/linux/shrinker.h |  1 +
 mm/vmscan.c              | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

-- 
2.4.5

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