Re: memleak in libfs report

[Chuck Lever III <chuck.lever@oracle.com>]

[ ... adding shmem maintainers ... ]

> On Oct 11, 2023, at 12:06 PM, Chuck Lever III <chuck.lever@oracle.com> wrote:
> 
>> On Oct 11, 2023, at 11:52 AM, Vlad Buslov <vladbu@nvidia.com> wrote:
>> 
>> On Wed 11 Oct 2023 at 15:34, Chuck Lever III <chuck.lever@oracle.com> wrote:
>>>> On Oct 11, 2023, at 11:15 AM, Vlad Buslov <vladbu@nvidia.com> wrote:
>>>> 
>>>> Hello Chuck,
>>>> 
>>>> We have been getting memleaks in offset_ctx->xa in our networking tests:
>>>> 
>>>> unreferenced object 0xffff8881004cd080 (size 576):
>>>> comm "systemd", pid 1, jiffies 4294893373 (age 1992.864s)
>>>> hex dump (first 32 bytes):
>>>>  00 00 06 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>>>>  38 5c 7c 02 81 88 ff ff 98 d0 4c 00 81 88 ff ff  8\|.......L.....
>>>> backtrace:
>>>>  [<000000000f554608>] xas_alloc+0x306/0x430
>>>>  [<0000000075537d52>] xas_create+0x4b4/0xc80
>>>>  [<00000000a927aab2>] xas_store+0x73/0x1680
>>>>  [<0000000020a61203>] __xa_alloc+0x1d8/0x2d0
>>>>  [<00000000ae300af2>] __xa_alloc_cyclic+0xf1/0x310
>>>>  [<000000001032332c>] simple_offset_add+0xd8/0x170
>>>>  [<0000000073229fad>] shmem_mknod+0xbf/0x180
>>>>  [<00000000242520ce>] vfs_mknod+0x3b0/0x5c0
>>>>  [<000000001ef218dd>] unix_bind+0x2c2/0xdb0
>>>>  [<0000000009b9a8dd>] __sys_bind+0x127/0x1e0
>>>>  [<000000003c949fbb>] __x64_sys_bind+0x6e/0xb0
>>>>  [<00000000b8a767c7>] do_syscall_64+0x3d/0x90
>>>>  [<000000006132ae0d>] entry_SYSCALL_64_after_hwframe+0x46/0xb0
>>>> 
>>>> It looks like those may be caused by recent commit 6faddda69f62 ("libfs:
>>>> Add directory operations for stable offsets")
>>> 
>>> That sounds plausible.
>>> 
>>> 
>>>> but we don't have a proper
>>>> reproduction, just sometimes arbitrary getting the memleak complains
>>>> during/after the regression run.
>>> 
>>> If the leak is a trickle rather than a flood, than can you take
>>> some time to see if you can narrow down a reproducer? If it's a
>>> flood, I can look at this immediately.
>> 
>> No, it is not a flood, we are not getting setups ran out of memory
>> during testing or anything. However, I don't have any good idea how to
>> narrow down the repro since as you can see from memleak trace it is a
>> result of some syscall performed by systemd and none of our tests do
>> anything more advanced with it than 'systemctl restart ovs-vswitchd'.
>> Basically it is a setup with Fedora and an upstream kernel that executes
>> bunch of network offload tests with Open vSwitch, iproute2 tc, Linux
>> bridge, etc.
> 
> OK, I'll see what I can do for a reproducer. Thank you for the
> report.

I've had kmemleak enabled on several systems for a week, and there
have been no tmpfs-related leaks detected. That suggests we don't
have a problem with normal workloads.

My next step is to go look at the ovs-vswitchd.service unit to
see if there are any leads there. We might ask Lennart or the
VSwitch folks if they have any suggestions too.

Meantime, can I ask that you open a bug on bugzilla.kernel.org
where we can collect troubleshooting information? Looks like
"Memory Management / Other" is appropriate for shmem, and Hugh
or Andrew can re-assign ownership to me.


--
Chuck Lever