| Message ID | 20220327051853.57647-1-songmuchun@bytedance.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] mm: kfence: fix missing objcg housekeeping for SLAB | expand |
On Mon, Mar 28, 2022 at 5:08 AM Linus Torvalds <torvalds@linux-foundation.org> wrote: > > On Sat, Mar 26, 2022 at 10:19 PM Muchun Song <songmuchun@bytedance.com> wrote: > > > > The objcg is not cleared and put for kfence object when it is freed, which > > could lead to memory leak for struct obj_cgroup and wrong statistics of > > NR_SLAB_RECLAIMABLE_B or NR_SLAB_UNRECLAIMABLE_B. Since the last freed > > object's objcg is not cleared, mem_cgroup_from_obj() could return the wrong > > memcg when this kfence object, which is not charged to any objcgs, is > > reallocated to other users. A real word issue [1] is caused by this bug. > > Good that this looks sorted out. > > Patch 2/2 seems to still be up in the air. The patch not only causes > build errors, but it looks really very odd to me. > > In particular, you do that loop with > > __SetPageSlab(&pages[i]); > > in kfence_init_pool(), but that is *not* where you set the > MEMCG_DATA_OBJCGS, and instead do that virt_to_slab(addr) dance later. > > That looks very odd to me. I think the two should go hand-in-hand, > since that __SetPageSlab() really is what makes it a slab thing, and I > think it should go together with setting the slab state correctly. Right. It is a little odd. I'll improve it in the next version. > > Finally, is there a syzbot report for that second problem? No. The second bug does not trigger any oops, so it is hard to be seen. It is just my code review. > > Anyway, should I apply this PATCH 1/2 now directly as the solution for > the dentry issue, or should I wait for that second patch? They seem to > be related only indirectly, in that the problems were both introduced > by the same commit. > I think you could apply PATCH 1/2 now. PATCH 2/2 is another issue not related to dentry issue. Thanks.
diff --git a/mm/slab.c b/mm/slab.c index d9dec7a8fd79..b04e40078bdf 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -3422,6 +3422,7 @@ static __always_inline void __cache_free(struct kmem_cache *cachep, void *objp, if (is_kfence_address(objp)) { kmemleak_free_recursive(objp, cachep->flags); + memcg_slab_free_hook(cachep, &objp, 1); __kfence_free(objp); return; }
The objcg is not cleared and put for kfence object when it is freed, which could lead to memory leak for struct obj_cgroup and wrong statistics of NR_SLAB_RECLAIMABLE_B or NR_SLAB_UNRECLAIMABLE_B. Since the last freed object's objcg is not cleared, mem_cgroup_from_obj() could return the wrong memcg when this kfence object, which is not charged to any objcgs, is reallocated to other users. A real word issue [1] is caused by this bug. [1] https://groups.google.com/g/syzkaller-bugs/c/BBQFy2QraoY/m/HtBd5gbyAQAJ Reported-by: syzbot+f8c45ccc7d5d45fc5965@syzkaller.appspotmail.com Fixes: d3fb45f370d9 ("mm, kfence: insert KFENCE hooks for SLAB") Signed-off-by: Muchun Song <songmuchun@bytedance.com> --- mm/slab.c | 1 + 1 file changed, 1 insertion(+)