Re: [PATCH v2 7/7] kunit, slub: add test_kfree_rcu() and test_leak_destroy()

[Hyeonggon Yoo]

On Wed, Aug 7, 2024 at 7:31 PM Vlastimil Babka <vbabka@xxxxxxx> wrote:
>
> Add a test that will create cache, allocate one object, kfree_rcu() it
> and attempt to destroy it. As long as the usage of kvfree_rcu_barrier()
> in kmem_cache_destroy() works correctly, there should be no warnings in
> dmesg and the test should pass.
>
> Additionally add a test_leak_destroy() test that leaks an object on
> purpose and verifies that kmem_cache_destroy() catches it.
>
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
>  lib/slub_kunit.c | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
>

Hi Vlastimil,

I think we might need to suppress the WARN() due to the active objects
in kmem_cache_destroy()
when it's called from slub_kunit. With this change, the warning below
will be printed every time
slub_kunit is loaded, which made me wonder if there's a bug (for a while).

Actually, SLUB calls pr_err() is called by __kmem_cache_shutdown() if
there are any active objects
during destruction, and the error message is suppressed by slub_kunit.
However, kmem_cache_destroy()
still calls WARN() regardless if there is any error during shutdown.

[  147.546531] Object 0x00000000c09342ca @offset=640
[  147.546542] ------------[ cut here ]------------
[  147.546544] kmem_cache_destroy TestSlub_kfree_rcu: Slab cache still
has objects when called from test_leak_destroy+0x74/0x108 [slub_kunit]
[  147.546579] WARNING: CPU: 5 PID: 39703 at mm/slab_common.c:507
kmem_cache_destroy+0x174/0x188
[  147.546587] Modules linked in: slub_kunit uinput snd_seq_dummy
snd_hrtimer rfkill nf_conntrack_netbios_ns nf_conntrack_broadcast
nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet
nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct sunrpc nft_chain_nat
nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set nf_tables
nfnetlink qrtr binfmt_misc vfat fat snd_hda_codec_generic
snd_hda_intel snd_intel_dspcfg snd_hda_codec uvcvideo snd_hda_core uvc
snd_hwdep videobuf2_vmalloc snd_seq videobuf2_memops snd_seq_device
videobuf2_v4l2 snd_pcm videobuf2_common snd_timer snd videodev mc
soundcore virtio_balloon acpi_tad joydev loop zram virtio_gpu
ahci_platform libahci_platform virtio_dma_buf crct10dif_ce polyval_ce
polyval_generic ghash_ce sha3_ce virtio_net sha512_ce net_failover
sha512_arm64 failover virtio_mmio ip6_tables ip_tables fuse
[  147.546646] CPU: 5 UID: 0 PID: 39703 Comm: kunit_try_catch Tainted:
G                 N 6.11.0-rc7-next-20240912 #2
[  147.546649] Tainted: [N]=TEST
[  147.546650] Hardware name: Parallels International GmbH. Parallels
ARM Virtual Machine/Parallels ARM Virtual Platform, BIOS 20.0.0
(55653) Thu, 05 Sep 202
[  147.546652] pstate: 61400005 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
[  147.546655] pc : kmem_cache_destroy+0x174/0x188
[  147.546657] lr : kmem_cache_destroy+0x174/0x188
[  147.546659] sp : ffff80008aba3d60
[  147.546660] x29: ffff80008aba3d60 x28: 0000000000000000 x27: 0000000000000000
[  147.546662] x26: 0000000000000000 x25: 0000000000000000 x24: ffff800094a2b438
[  147.546665] x23: ffff80008089b750 x22: 0000000000000001 x21: f9cc80007c1782f4
[  147.546666] x20: ffff800082f9d088 x19: ffff0000c2308b00 x18: 00000000fffffffd
[  147.546668] x17: 0000000046d4ed9c x16: 00000000ae1ad4db x15: ffff80008aba3430
[  147.546670] x14: 0000000000000001 x13: ffff80008aba3657 x12: ffff800082f0f060
[  147.546679] x11: 0000000000000001 x10: 0000000000000001 x9 : ffff8000801652c8
[  147.546682] x8 : c0000000ffffdfff x7 : ffff800082e5ee68 x6 : 00000000000affa8
[  147.546684] x5 : ffff00031fc70448 x4 : 0000000000000000 x3 : ffff80029d6b7000
[  147.546686] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff00011f1c8000
[  147.546688] Call trace:
[  147.546689]  kmem_cache_destroy+0x174/0x188
[  147.546692]  test_leak_destroy+0x74/0x108 [slub_kunit]
[  147.546693]  kunit_try_run_case+0x74/0x170
[  147.546697]  kunit_generic_run_threadfn_adapter+0x30/0x60
[  147.546699]  kthread+0xf4/0x108
[  147.546705]  ret_from_fork+0x10/0x20
[  147.546710] ---[ end trace 0000000000000000 ]---