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Mon, 14 Oct 2024 17:04:26 +0800 Message-ID: <1dc9acbd-351f-4755-8c56-d3d77aaccfb2@huawei.com> Date: Mon, 14 Oct 2024 17:04:24 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: shrinker: avoid memleak in alloc_shrinker_info To: Muchun Song , Anshuman Khandual , Chen Ridong CC: , , , , , , References: <20241014032336.482088-1-chenridong@huaweicloud.com> <178A7AC8-0BDA-42CA-86B2-E1C13F3E1E8B@linux.dev> Content-Language: en-US From: chenridong In-Reply-To: <178A7AC8-0BDA-42CA-86B2-E1C13F3E1E8B@linux.dev> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.67.109.79] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To kwepemd100013.china.huawei.com (7.221.188.163) X-Rspamd-Queue-Id: B68DD4000C X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: ogdm5tn8gjxfwttja6k5f1ac9c1of5kd X-HE-Tag: 1728896665-580082 X-HE-Meta: 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 rcQZijCo GlnhMhGXcHtlwDcZhA89ivSf6k0D3udQTGuI8GJsqhgxeaDhgBaknWm/NbBxOc0b20Q55Srhm0dGVwTAwBu97peb04fJH0hTxp4TtRvrCxLxHhRPihxAtNFASxoyeegkv4c8nP8jClDBSJ5UnjJCfLSV+3jP1EIs7gL5BVeQ3G/KRhPR9xPvHgKFO7oFqAZ/G/YmDvfTfkJbZ5pf5PezYvVx8H0QZ63Jka/8YvUUBAIvR3Fv5KWwLflNx5ClH8cAj8s9RZ1w3npG+aGxjnb90EYB2DtvgR4+ZHMn7YM3xIiBc8QQ= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2024/10/14 16:43, Muchun Song wrote: > > >> On Oct 14, 2024, at 16:13, Anshuman Khandual wrote: >> >> >> >> On 10/14/24 08:53, 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 shrinker_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; >>> } >> >> There are two scenarios when "goto err:" gets called >> >> - 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. > >> >> - shrinker_unit_alloc() fails, kvfree() is actually required >> >> 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 = 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. > >> >> But curious, should not both kvzalloc_node()/kvfree() be avoided >> while inside mutex lock to avoid possible lockdep issues ? > How about: 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 = 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); I think this is concise. Best regards, Ridong