On 2024/10/16 22:22, Muchun Song wrote:
On Oct 16, 2024, at 20:13, Vlastimil Babka <vbabka@xxxxxxx> wrote:
On 10/14/24 11:20, Muchun Song wrote:
On Oct 14, 2024, at 17:04, chenridong <chenridong@xxxxxxxxxx> wrote:
On 2024/10/14 16:43, Muchun Song wrote:
On Oct 14, 2024, at 16:13, Anshuman Khandual <anshuman.khandual@xxxxxxx> wrote:
On 10/14/24 08:53, Chen Ridong wrote:
From: Chen Ridong <chenridong@xxxxxxxxxx>
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):
[<ffffffff81372754>] __kmalloc_node_noprof+0x394/0x470
[<ffffffff813024ab>] alloc_shrinker_info+0x7b/0x1a0
[<ffffffff813b526a>] mem_cgroup_css_online+0x11a/0x3b0
[<ffffffff81198dd9>] online_css+0x29/0xa0
[<ffffffff811a243d>] cgroup_apply_control_enable+0x20d/0x360
[<ffffffff811a5728>] cgroup_mkdir+0x168/0x5f0
[<ffffffff8148543e>] kernfs_iop_mkdir+0x5e/0x90
[<ffffffff813dbb24>] vfs_mkdir+0x144/0x220
[<ffffffff813e1c97>] do_mkdirat+0x87/0x130
[<ffffffff813e1de9>] __x64_sys_mkdir+0x49/0x70
[<ffffffff81f8c928>] do_syscall_64+0x68/0x140
[<ffffffff8200012f>] 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 <chenridong@xxxxxxxxxx>
---
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);
No. We should make sure the @info is fully initialized before others
could see it. That's why rcu_assign_pointer is used here.
If the info is immediately visible, is the failure cleanup
free_shrinker_info() safe? It uses kvfree(info) and not kvfree_rcu(), and
shrinker_unit_free() is also doing kfree().
Qi told me that the @info will not visible immediately yesterday.
So non-rcu-based kvfree is safe. Even if this fix could
Yes, alloc_shrinker_info() is only called by mem_cgroup_css_online(). At
this time, the memcg is not online yet, so it is not visible to
shrink_slab(). And free_shrinker_info() is also called by
mem_cgroup_css_free(),
the memcg has already been offline. The shrinker_unit_free() is
also called by expand_one_shrinker_info(), but the shrinker_info 'new'
is also not visible at that time. So non-rcu-based kvfree is safe.
work properly, it’s a bit strange for me to use
rcu_assign_pointer to assign the @info without full initialization to it.
Agree.
Muchun,
Thanks.
I think this is concise.
Best regards,
Ridong
