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From: Muchun Song In-Reply-To: Cc: chenridong , Anshuman Khandual , "Kirill A. Shutemov" , akpm@linux-foundation.org, david@fromorbit.com, zhengqi.arch@bytedance.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, wangweiyang2@huawei.com Date: Wed, 16 Oct 2024 22:08:27 +0800 Message-Id: <1BD74B20-879A-4159-B957-1223553217C1@linux.dev> References: To: Vlastimil Babka X-Migadu-Flow: FLOW_OUT > On Oct 16, 2024, at 19:43, Vlastimil Babka wrote: > =EF=BB=BFOn 10/16/24 04:21, Muchun Song wrote: >>=20 >>=20 >>> On Oct 16, 2024, at 09:25, chenridong wrote: >>> On 2024/10/15 14:55, Anshuman Khandual wrote: >>>> On 10/14/24 16:59, Kirill A. Shutemov wrote: >>>>> On Mon, Oct 14, 2024 at 03:23:36AM +0000, Chen Ridong wrote: >>>>>> From: Chen Ridong >>>>>> A memleak was found as bellow: >>>>>> unreferenced object 0xffff8881010d2a80 (size 32): >>>>>> comm "mkdir", pid 1559, jiffies 4294932666 >>>>>> hex dump (first 32 bytes): >>>>>> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ >>>>>> 40 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 @............... >>>>>> backtrace (crc 2e7ef6fa): >>>>>> [] __kmalloc_node_noprof+0x394/0x470 >>>>>> [] alloc_shrinker_info+0x7b/0x1a0 >>>>>> [] mem_cgroup_css_online+0x11a/0x3b0 >>>>>> [] online_css+0x29/0xa0 >>>>>> [] cgroup_apply_control_enable+0x20d/0x360 >>>>>> [] cgroup_mkdir+0x168/0x5f0 >>>>>> [] kernfs_iop_mkdir+0x5e/0x90 >>>>>> [] vfs_mkdir+0x144/0x220 >>>>>> [] do_mkdirat+0x87/0x130 >>>>>> [] __x64_sys_mkdir+0x49/0x70 >>>>>> [] do_syscall_64+0x68/0x140 >>>>>> [] entry_SYSCALL_64_after_hwframe+0x76/0x7e >>>>>> In the alloc_shrinker_info function, when shrinker_unit_alloc return >>>>>> err, the info won't be freed. Just fix it. >>>>>> Fixes: 307bececcd12 ("mm: shrinker: add a secondary array for shrinke= r_info::{map, nr_deferred}") >>>>>> Signed-off-by: Chen Ridong >>>>>> --- >>>>>> mm/shrinker.c | 1 + >>>>>> 1 file changed, 1 insertion(+) >>>>>> diff --git a/mm/shrinker.c b/mm/shrinker.c >>>>>> index dc5d2a6fcfc4..92270413190d 100644 >>>>>> --- a/mm/shrinker.c >>>>>> +++ b/mm/shrinker.c >>>>>> @@ -97,6 +97,7 @@ int alloc_shrinker_info(struct mem_cgroup *memcg) >>>>>> err: >>>>>> mutex_unlock(&shrinker_mutex); >>>>>> + kvfree(info); >>>>>> free_shrinker_info(memcg); >>>>>> return -ENOMEM; >>>>>> } >>>>> NAK. If in the future there going to one more error case after >>>>> rcu_assign_pointer() we will end up with double free. >>>>> This should be safer: >>>>> diff --git a/mm/shrinker.c b/mm/shrinker.c >>>>> index dc5d2a6fcfc4..763fd556bc7d 100644 >>>>> --- a/mm/shrinker.c >>>>> +++ b/mm/shrinker.c >>>>> @@ -87,8 +87,10 @@ int alloc_shrinker_info(struct mem_cgroup *memcg) >>>>> if (!info) >>>>> goto err; >>>>> info->map_nr_max =3D shrinker_nr_max; >>>>> - if (shrinker_unit_alloc(info, NULL, nid)) >>>>> + if (shrinker_unit_alloc(info, NULL, nid)) { >>>>> + kvfree(info); >>>>> goto err; >>>>> + } >>>>> rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info); >>>>> } >>>>> mutex_unlock(&shrinker_mutex); >>>> Agreed, this is what I mentioned earlier as well. >>>> ------------------------------------------------------------------ >>>> I guess kvfree() should be called just after shrinker_unit_alloc() >>>> fails but before calling into "goto err" >>>> ------------------------------------------------------------------ >>> After discussion, it seems that v1 is acceptable. >>> Hi, Muchun, do you have any other opinions? >>=20 >> I insist on my opinion, not mixing two different approaches >> to do release resources. >=20 > So instead we mix the cleanup of the whole function with the cleanup of wh= at > is effectively a per-iteration temporary variable? >=20 > The fact there was already a confusion in this thread about whether it's > safe and relies on kvfree(NULL) to be a no-op, should be a hint. Yes. I think someone is confused about my opinion. I don=E2=80=99t care about whether we should apply this hit. If we think the hint is tricky, we could add another label to fix it like I suggested previously. Because we already use goto-based approaches to cleanup the resources, why not keeping consistent? It will be easier for us to add a new "if" statement and handle the failure case in the future. For example, if we use his v1 proposal, we should do the cleanups again for info. But for goto-based version, we just add another label to do the cleanups and go to the new label for failure case. goto-based fix is what I i= nsisted on. I copied my previous suggested fix here to clarify my opinion. --- a/mm/shrinker.c +++ b/mm/shrinker.c @@ -88,13 +88,14 @@ int alloc_shrinker_info(struct mem_cgroup *memcg) goto err; info->map_nr_max =3D shrinker_nr_max; if (shrinker_unit_alloc(info, NULL, nid)) - goto err; + goto free; rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);= } mutex_unlock(&shrinker_mutex); return ret; - +free: + kvfree(info); err: mutex_unlock(&shrinker_mutex); free_shrinker_info(memcg); Muchun, Thanks. >=20 > So no, I a gree with Kirill and others. Ideally the fix would also move th= e > declaration of info into the for loop to make its scope more obvious. >=20 >> Thanks. >>=20 >>> Best regards, >>> Ridong