On Wed, Oct 16, 2024 at 10:21:30AM +0800, Muchun Song wrote:
>
>
> > On Oct 16, 2024, at 09:25, chenridong <chenridong@xxxxxxxxxx> 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 <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;
> >>>> }
> >>>
> >>> 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 = 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?
>
> I insist on my opinion, not mixing two different approaches
> to do release resources.
It makes no sense.
This kvfree() is specifically to handle the case when 'info' is allocated,
but not yet assigned to ->shrinker_info. And 'err:' block handles all
other error cases. Putting kvfree() in 'err:' section is double-free
timebomb.
--
Kiryl Shutsemau / Kirill A. Shutemov
