| Message ID | 20241206225204.4008261-6-surenb@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | move per-vma lock into vm_area_struct | expand |
On 12/6/24 23:52, Suren Baghdasaryan wrote: > There is no real reason to prevent freeptr_offset usage when a slab > cache has a ctor. The only real limitation is that any field unioned > with the free pointer and initialized by ctor will be overwritten since > free pointer is set after @ctor invocation. Document this limitation > and enable usage of freeptr_offset with ctor. > > Suggested-by: Vlastimil Babka <vbabka@suse.cz> > Signed-off-by: Suren Baghdasaryan <surenb@google.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> > --- > include/linux/slab.h | 5 +++-- > mm/slub.c | 2 +- > 2 files changed, 4 insertions(+), 3 deletions(-) > > diff --git a/include/linux/slab.h b/include/linux/slab.h > index 681b685b6c4e..6bad744bef5e 100644 > --- a/include/linux/slab.h > +++ b/include/linux/slab.h > @@ -305,8 +305,9 @@ struct kmem_cache_args { > * Using %0 as a value for @freeptr_offset is valid. If @freeptr_offset > * is specified, %use_freeptr_offset must be set %true. > * > - * Note that @ctor currently isn't supported with custom free pointers > - * as a @ctor requires an external free pointer. > + * Note that fields unioned with free pointer cannot be initialized by > + * @ctor since free pointer is set after @ctor invocation, so those > + * values will be overwritten. > */ > unsigned int freeptr_offset; > /** > diff --git a/mm/slub.c b/mm/slub.c > index 870a1d95521d..f62c829b7b6b 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5462,7 +5462,7 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s) > s->inuse = size; > > if (((flags & SLAB_TYPESAFE_BY_RCU) && !args->use_freeptr_offset) || > - (flags & SLAB_POISON) || s->ctor || > + (flags & SLAB_POISON) || (s->ctor && !args->use_freeptr_offset) || > ((flags & SLAB_RED_ZONE) && > (s->object_size < sizeof(void *) || slub_debug_orig_size(s)))) { > /*
diff --git a/include/linux/slab.h b/include/linux/slab.h index 681b685b6c4e..6bad744bef5e 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -305,8 +305,9 @@ struct kmem_cache_args { * Using %0 as a value for @freeptr_offset is valid. If @freeptr_offset * is specified, %use_freeptr_offset must be set %true. * - * Note that @ctor currently isn't supported with custom free pointers - * as a @ctor requires an external free pointer. + * Note that fields unioned with free pointer cannot be initialized by + * @ctor since free pointer is set after @ctor invocation, so those + * values will be overwritten. */ unsigned int freeptr_offset; /** diff --git a/mm/slub.c b/mm/slub.c index 870a1d95521d..f62c829b7b6b 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -5462,7 +5462,7 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s) s->inuse = size; if (((flags & SLAB_TYPESAFE_BY_RCU) && !args->use_freeptr_offset) || - (flags & SLAB_POISON) || s->ctor || + (flags & SLAB_POISON) || (s->ctor && !args->use_freeptr_offset) || ((flags & SLAB_RED_ZONE) && (s->object_size < sizeof(void *) || slub_debug_orig_size(s)))) { /*
There is no real reason to prevent freeptr_offset usage when a slab cache has a ctor. The only real limitation is that any field unioned with the free pointer and initialized by ctor will be overwritten since free pointer is set after @ctor invocation. Document this limitation and enable usage of freeptr_offset with ctor. Suggested-by: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Suren Baghdasaryan <surenb@google.com> --- include/linux/slab.h | 5 +++-- mm/slub.c | 2 +- 2 files changed, 4 insertions(+), 3 deletions(-)