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From: Muchun Song In-Reply-To: <1dc9acbd-351f-4755-8c56-d3d77aaccfb2@huawei.com> Date: Mon, 14 Oct 2024 17:20:34 +0800 Cc: Anshuman Khandual , Chen Ridong , 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 Content-Transfer-Encoding: quoted-printable Message-Id: References: <20241014032336.482088-1-chenridong@huaweicloud.com> <178A7AC8-0BDA-42CA-86B2-E1C13F3E1E8B@linux.dev> <1dc9acbd-351f-4755-8c56-d3d77aaccfb2@huawei.com> To: chenridong X-Migadu-Flow: FLOW_OUT > On Oct 14, 2024, at 17:04, chenridong wrote: >=20 >=20 >=20 > On 2024/10/14 16:43, Muchun Song wrote: >>> On Oct 14, 2024, at 16:13, Anshuman Khandual = wrote: >>>=20 >>>=20 >>>=20 >>> On 10/14/24 08:53, Chen Ridong wrote: >>>> From: Chen Ridong >>>>=20 >>>> A memleak was found as bellow: >>>>=20 >>>> 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 >>>>=20 >>>> In the alloc_shrinker_info function, when shrinker_unit_alloc = return >>>> err, the info won't be freed. Just fix it. >>>>=20 >>>> Fixes: 307bececcd12 ("mm: shrinker: add a secondary array for = shrinker_info::{map, nr_deferred}") >>>> Signed-off-by: Chen Ridong >>>> --- >>>> mm/shrinker.c | 1 + >>>> 1 file changed, 1 insertion(+) >>>>=20 >>>> 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) >>>>=20 >>>> err: >>>> mutex_unlock(&shrinker_mutex); >>>> + kvfree(info); >>>> free_shrinker_info(memcg); >>>> return -ENOMEM; >>>> } >>>=20 >>> There are two scenarios when "goto err:" gets called >>>=20 >>> - When shrinker_info allocations fails, no kvfree() is required >>> - but after this change kvfree() would be called even >>> when the allocation had failed originally, which does >>> not sound right >> Yes. In this case, @info is NULL and kvfree could handle NULL. >> It seems strange but the final behaviour correct. >>>=20 >>> - shrinker_unit_alloc() fails, kvfree() is actually required >>>=20 >>> I guess kvfree() should be called just after shrinker_unit_alloc() >>> fails but before calling into "goto err". >> We could do it like this, which avoids ambiguity (if someone ignores >> that kvfree could handle NULL). Something like: >> --- 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); >> Thanks. >>>=20 >>> But curious, should not both kvzalloc_node()/kvfree() be avoided >>> while inside mutex lock to avoid possible lockdep issues ? > How about: >=20 > diff --git a/mm/shrinker.c b/mm/shrinker.c > index dc5d2a6fcfc4..7baee7f00497 100644 > --- a/mm/shrinker.c > +++ b/mm/shrinker.c > @@ -87,9 +87,9 @@ int alloc_shrinker_info(struct mem_cgroup *memcg) > if (!info) > goto err; > info->map_nr_max =3D shrinker_nr_max; > + = rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info); > if (shrinker_unit_alloc(info, NULL, nid)) > goto err; > - = rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info); > } > mutex_unlock(&shrinker_mutex); No. We should make sure the @info is fully initialized before others could see it. That's why rcu_assign_pointer is used here. >=20 > I think this is concise. >=20 > Best regards, > Ridong