On Wed, Jul 28, 2021 at 06:44:03PM +0200, Michal Hocko wrote:
> On Wed 28-07-21 22:56:55, Wang Hai wrote:
> > When I use kfree_rcu() to free a large memory allocated by
> > kmalloc_node(), the following dump occurs.
> >
> > BUG: kernel NULL pointer dereference, address: 0000000000000020
> > [...]
> > Oops: 0000 [#1] SMP
> > [...]
> > Workqueue: events kfree_rcu_work
> > RIP: 0010:__obj_to_index include/linux/slub_def.h:182 [inline]
> > RIP: 0010:obj_to_index include/linux/slub_def.h:191 [inline]
> > RIP: 0010:memcg_slab_free_hook+0x120/0x260 mm/slab.h:363
> > [...]
> > Call Trace:
> > kmem_cache_free_bulk+0x58/0x630 mm/slub.c:3293
> > kfree_bulk include/linux/slab.h:413 [inline]
> > kfree_rcu_work+0x1ab/0x200 kernel/rcu/tree.c:3300
> > process_one_work+0x207/0x530 kernel/workqueue.c:2276
> > worker_thread+0x320/0x610 kernel/workqueue.c:2422
> > kthread+0x13d/0x160 kernel/kthread.c:313
> > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
> >
> > When kmalloc_node() a large memory, page is allocated, not slab,
> > so when freeing memory via kfree_rcu(), this large memory should not
> > be used by memcg_slab_free_hook(), because memcg_slab_free_hook() is
> > is used for slab.
> >
> > Using page_objcgs_check() instead of page_objcgs() in
> > memcg_slab_free_hook() to fix this bug.
> >
> > Fixes: 270c6a71460e ("mm: memcontrol/slab: Use helpers to access slab page's memcg_data")
> > Signed-off-by: Wang Hai <wanghai38@xxxxxxxxxx>
>
> This looks like a much better fix. Thanks!
+1
Acked-by: Roman Gushchin <guro@xxxxxx>
Thank you, Wang!
