Messages in this thread | | | Subject | Re: [PATCH] mm/memcg: fix NULL pointer dereference in memcg_slab_free_hook() | From | "wanghai (M)" <> | Date | Wed, 28 Jul 2021 22:33:54 +0800 |
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在 2021/7/28 22:26, Shakeel Butt 写道: > On Wed, Jul 28, 2021 at 7:21 AM Kefeng Wang <wangkefeng.wang@huawei.com> wrote: >> >> On 2021/7/28 21:23, Michal Hocko wrote: >>> On Wed 28-07-21 17:13:48, 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. >>>> >>>> So in this case, there is no need to do anything with this large >>>> page in memcg_slab_free_hook(), just skip it. >>>> >>>> Fixes: 270c6a71460e ("mm: memcontrol/slab: Use helpers to access slab page's memcg_data") >>> Are you sure that this commit is really breaking the code. Unless I have >> Yes, we confirmed that this commit introduces the bug. >>> missed something there shouldn't be any real change wrt. large >>> allocations here. page_has_obj_cgroups is just a different name for what >>> what page_objcgs is giving us. >> maybe we could simply use page_objcgs_check to fix the issue ? we will >> check it again. > You will see the same crash with page_objcgs_check as well. > .
I just test it. It won't crash.
This is the test case:
node = kmalloc_node(299999, GFP_ATOMIC | __GFP_NOWARN | __GFP_ACCOUNT, -1); kfree_rcu(node, rcu);
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