Re: [PATCH] mm/slab: Fix a kmemleak in kmem_cache_destroy()

[xiaolei wang]

On 2/28/24 15:34, Vlastimil Babka wrote:
> CAUTION: This email comes from a non Wind River email account!
> Do not click links or open attachments unless you recognize the sender and know the content is safe.
>
> On 2/28/24 04:04, Xiaolei Wang wrote:
> > For earlier kmem cache creation, slab_sysfs_init() has not been called.
> > Consequently, kmem_cache_destroy() cannot utilize kobj_type::release to
> > release the kmem_cache structure. Therefore, tweak kmem_cache_release()
> > to use slab_kmem_cache_release() for releasing kmem_cache when slab_state
> > isn't FULL. This will fixes the memory leaks like following:
> So do I understand correctly the leak happens when a cache is destroyed
> while slab_state < FULL? Do we ever destroy a cache that early?

Yes, like some test programs, test_meminit_init() or 
arm_v7s_alloc_pgtable(),

destroy will cause leaks after use, and when slab_state < FULL,

there are many places to create cache, which itself also has the risk of 
leaks

thanks

xiaolei

> > unreferenced object 0xffff0000c2d87080 (size 128):
> >     comm "swapper/0", pid 1, jiffies 4294893428
> >     hex dump (first 32 bytes):
> >       00 00 00 00 ad 4e ad de ff ff ff ff 6b 6b 6b 6b .....N......kkkk
> >       ff ff ff ff ff ff ff ff b8 ab 48 89 00 80 ff ff.....H.....
> >     backtrace (crc 8819d0f6):
> >       [<ffff80008317a298>] kmemleak_alloc+0xb0/0xc4
> >       [<ffff8000807e553c>] kmem_cache_alloc_node+0x288/0x3a8
> >       [<ffff8000807e95f0>] __kmem_cache_create+0x1e4/0x64c
> >       [<ffff8000807216bc>] kmem_cache_create_usercopy+0x1c4/0x2cc
> >       [<ffff8000807217e0>] kmem_cache_create+0x1c/0x28
> >       [<ffff8000819f6278>] arm_v7s_alloc_pgtable+0x1c0/0x6d4
> >       [<ffff8000819f53a0>] alloc_io_pgtable_ops+0xe8/0x2d0
> >       [<ffff800084b2d2c4>] arm_v7s_do_selftests+0xe0/0x73c
> >       [<ffff800080016b68>] do_one_initcall+0x11c/0x7ac
> >       [<ffff800084a71ddc>] kernel_init_freeable+0x53c/0xbb8
> >       [<ffff8000831728d8>] kernel_init+0x24/0x144
> >       [<ffff800080018e98>] ret_from_fork+0x10/0x20
> >
> > Signed-off-by: Xiaolei Wang <xiaolei.wang@xxxxxxxxxxxxx>
> > ---
> >   mm/slab_common.c | 8 ++++++--
> >   mm/slub.c        | 6 ++----
> >   2 files changed, 8 insertions(+), 6 deletions(-)
> >
> > diff --git a/mm/slab_common.c b/mm/slab_common.c
> > index 238293b1dbe1..b6b35bcdd196 100644
> > --- a/mm/slab_common.c
> > +++ b/mm/slab_common.c
> > @@ -404,8 +404,12 @@ EXPORT_SYMBOL(kmem_cache_create);
> >    */
> >   static void kmem_cache_release(struct kmem_cache *s)
> >   {
> > -     sysfs_slab_unlink(s);
> > -     sysfs_slab_release(s);
> > +     if (slab_state >= FULL) {
> > +             sysfs_slab_unlink(s);
> > +             sysfs_slab_release(s);
> > +     } else {
> > +             slab_kmem_cache_release(s);
> > +     }
> >   }
> >   #else
> >   static void kmem_cache_release(struct kmem_cache *s)
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 2ef88bbf56a3..9ba59d064b6d 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -6792,14 +6792,12 @@ static int sysfs_slab_add(struct kmem_cache *s)
> >
> >   void sysfs_slab_unlink(struct kmem_cache *s)
> >   {
> > -     if (slab_state >= FULL)
> > -             kobject_del(&s->kobj);
> > +     kobject_del(&s->kobj);
> >   }
> >
> >   void sysfs_slab_release(struct kmem_cache *s)
> >   {
> > -     if (slab_state >= FULL)
> > -             kobject_put(&s->kobj);
> > +     kobject_put(&s->kobj);
> >   }
> >
> >   /*