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

[Yonghong Song]

On 2/11/18 11:18 AM, Mathieu Malaterre wrote:
> Hi,
>
> On Sun, Feb 11, 2018 at 5:54 PM, Alexei Starovoitov
> <alexei.starovoitov@xxxxxxxxx> wrote:
> > On Sun, Feb 11, 2018 at 7:24 AM, Mathieu Malaterre <malat@xxxxxxxxxx> 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.


>