Re: [kmemleak] unreferenced object 0xcd9c1a80 (size 192):

[Yonghong Song <yhs@fb.com>]

On 2/11/18 11:18 AM, Mathieu Malaterre wrote:
> Hi,
> 
> On Sun, Feb 11, 2018 at 5:54 PM, Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
>> On Sun, Feb 11, 2018 at 7:24 AM, Mathieu Malaterre <malat@debian.org> wrote:
>>> Alexei,
>>>
>>> Could you please comment on why I am seeing those memleaks being
>>> reported on my ppc32 system ? Should they be marked as false positive
>>> ?
>>>
>>> System is Mac Mini G4, git/master (4.15.0+), ppc.
>>>
>>> Thanks for your time
>>>
>>> $ dmesg
>>> ...
>>> [ 1281.504173] kmemleak: 36 new suspected memory leaks (see
>>> /sys/kernel/debug/kmemleak)
>>>
>>> Where:
>>>
>>> # cat /sys/kernel/debug/kmemleak
>>> unreferenced object 0xdee25000 (size 192):
>>>    comm "systemd", pid 1, jiffies 4294894348 (age 1438.580s)
>>>    hex dump (first 32 bytes):
>>>      c0 56 2f 88 00 00 00 00 00 00 00 0b 00 00 00 0c  .V/.............
>>>      00 00 00 08 00 00 00 01 00 00 00 01 00 00 00 01  ................
>>>    backtrace:
>>>      [<6c69baf5>] trie_alloc+0xb0/0x150
>>>      [<fa093284>] SyS_bpf+0x288/0x1458
>>>      [<82182f53>] ret_from_syscall+0x0/0x38
>>> unreferenced object 0xdee25900 (size 192):
>>>    comm "systemd", pid 1, jiffies 4294894540 (age 1437.812s)
>>>    hex dump (first 32 bytes):
>>>      c0 56 2f 88 00 00 00 00 00 00 00 0b 00 00 00 08  .V/.............
>>>      00 00 00 08 00 00 00 01 00 00 00 01 00 00 00 01  ................
>>>    backtrace:
>>>      [<6c69baf5>] trie_alloc+0xb0/0x150
>>>      [<fa093284>] SyS_bpf+0x288/0x1458
>>>      [<82182f53>] ret_from_syscall+0x0/0x38
>>
>> hmm. looks real. Is there a reproducer?
>> Yonghong, lpm map not cleaning after itself?
> 
> Not really. I simply boot up my machine and wait for the first kmemleak scan.

I am not able to reproduce the issue. Tried with latest net-next on FC26 
with kmemleak on. I only got this one after bootup,
'cat /sys/kernel/debug/kmemleak' or
'echo scan > /sys/kernel/debug/kmemleak
  cat /sys/kernel/debug/kmemleak':

unreferenced object 0xffff99701a7386e0 (size 32):
   comm "mount", pid 1856, jiffies 4294669263 (age 98.440s)
   hex dump (first 32 bytes):
     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
   backtrace:
     [<000000004668ec00>] security_sb_parse_opts_str+0x36/0x50
     [<00000000a9807d2b>] parse_security_options+0x3d/0x60
     [<00000000cc1e1d58>] btrfs_mount_root+0x139/0x720
     [<00000000bdc4f1a3>] mount_fs+0x30/0x150
     [<00000000f189f1bd>] vfs_kern_mount.part.26+0x54/0x100
     [<0000000093ae5db7>] btrfs_mount+0x184/0x914
     [<00000000bdc4f1a3>] mount_fs+0x30/0x150
     [<00000000f189f1bd>] vfs_kern_mount.part.26+0x54/0x100
     [<000000003b67b9fc>] do_mount+0x5b9/0xc70
     [<00000000de4073a0>] SyS_mount+0x80/0xd0
     [<00000000fc5a968a>] do_syscall_64+0x5d/0x110
     [<000000003d61f5fc>] entry_SYSCALL_64_after_hwframe+0x21/0x86
     [<00000000458a6ffa>] 0xffffffffffffffff

Not sure whether the above is a true issue or not.

However, by inspecting the code, I do find the trie_free in lpm_trie.c
may have missed freeing the trie memory.

The change likes below should work:
-bash-4.2$ git diff 

diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
index 7b469d1..cecb259 100644
--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -589,6 +589,7 @@ static void trie_free(struct bpf_map *map)

  unlock:
         raw_spin_unlock(&trie->lock);
+       kfree(trie);
  }

  static int trie_get_next_key(struct bpf_map *map, void *_key, void 
*_next_key)
-bash-4.2$

Will propose a formal patch for this soon.


>