On (07/10/15 18:33), Andrew Morton wrote:
> > > > I was thinking of a trivial INIT_SHRINKER macro to init `struct
> > > > shrinker'
> > > > internal members (composed in email client, not tested)
> > > >
> > > > include/linux/shrinker.h
> > > >
> > > > #define INIT_SHRINKER(s) \
> > > > do { \
> > > > (s)->nr_deferred = NULL; \
> > > > INIT_LIST_HEAD(&(s)->list); \
> > > > } while (0)
> > >
> > > Spose so. Although it would be simpler to change unregister_shrinker()
> > > to bale out if list.next==NULL and then say "all zeroes is the
> > > initialized state".
> >
> > Yes, or '->nr_deferred == NULL' -- we can't have NULL ->nr_deferred
> > in a properly registered shrinker (as of now)
>
> list.next seems safer because that will always be non-zero. But
> whatever - we can change it later.
>
> > But that will not work if someone has accidentally passed not zeroed
> > out pointer to unregister.
>
> I wouldn't worry about that really. If you pass a pointer to
> uninitialized memory, the kernel will explode. That's true of just
> about every pointer-accepting function in the kernel.
>
True. But with shrinker it's hard to say whether we have a properly
initialized shrinker embedded in our `struct foo' or we don't (unless
we treat register_shrinker() errors as a show stopper) by simply looking at
shrinker struct (w/o touching it's private members). In zsmalloc, for
instance, we don't consider failed register_shrinker() to be critical
enough to forbid zs_pool creation and usage. It makes things harder later
in zs_destroy_pool(), because we need to carry some sort of flag for that
purpose. But `list.next' check in unregister_shrinker() would suffice in
zsmalloc case, I must admit, because we kzalloc() the entire zs_pool
struct.
-ss
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