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

[Guenter Roeck <linux@roeck-us.net>]

Hi,

On Wed, Aug 07, 2024 at 12:31:20PM +0200, Vlastimil Babka 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@suse.cz>

This test case, when run, triggers a warning traceback.

kmem_cache_destroy TestSlub_kfree_rcu: Slab cache still has objects when called from test_leak_destroy+0x70/0x11c
WARNING: CPU: 0 PID: 715 at mm/slab_common.c:511 kmem_cache_destroy+0x1dc/0x1e4

That is, however, not the worst of it. It also causes boot stalls on
several platforms and architectures (various arm platforms, arm64,
loongarch, various ppc, and various x86_64). Reverting it fixes the
problem. Bisect results are attached for reference.

Guenter

---
# bad: [baeb9a7d8b60b021d907127509c44507539c15e5] Merge tag 'sched-rt-2024-09-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
# good: [2f27fce67173bbb05d5a0ee03dae5c021202c912] Merge tag 'sound-6.12-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound
git bisect start 'HEAD' '2f27fce67173'
# good: [ae2c6d8b3b88c176dff92028941a4023f1b4cb91] Merge tag 'drm-xe-next-fixes-2024-09-12' of https://gitlab.freedesktop.org/drm/xe/kernel into drm-next
git bisect good ae2c6d8b3b88c176dff92028941a4023f1b4cb91
# bad: [c8d8a35d094626808cd07ed0758e14c7e4cf61ac] Merge tag 'livepatching-for-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/livepatching/livepatching
git bisect bad c8d8a35d094626808cd07ed0758e14c7e4cf61ac
# bad: [cc52dc2fe39ff5dee9916ac2d9381ec3cbf650c0] Merge tag 'pwm/for-6.12-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/ukleinek/linux
git bisect bad cc52dc2fe39ff5dee9916ac2d9381ec3cbf650c0
# bad: [bdf56c7580d267a123cc71ca0f2459c797b76fde] Merge tag 'slab-for-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab
git bisect bad bdf56c7580d267a123cc71ca0f2459c797b76fde
# good: [355debb83bf79853cde43579f88eed16adb1da29] Merge branches 'context_tracking.15.08.24a', 'csd.lock.15.08.24a', 'nocb.09.09.24a', 'rcutorture.14.08.24a', 'rcustall.09.09.24a', 'srcu.12.08.24a', 'rcu.tasks.14.08.24a', 'rcu_scaling_tests.15.08.24a', 'fixes.12.08.24a' and 'misc.11.08.24a' into next.09.09.24a
git bisect good 355debb83bf79853cde43579f88eed16adb1da29
# good: [067610ebaaec53809794807842a2fcf5f1f5b9eb] Merge tag 'rcu.release.v6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux
git bisect good 067610ebaaec53809794807842a2fcf5f1f5b9eb
# good: [4b7ff9ab98af11a477d50f08382bcc4c2f899926] mm, slab: restore kerneldoc for kmem_cache_create()
git bisect good 4b7ff9ab98af11a477d50f08382bcc4c2f899926
# bad: [a715e94dbda4ece41aac49b7b7ff8ddb55a7fe08] Merge branch 'slab/for-6.12/rcu_barriers' into slab/for-next
git bisect bad a715e94dbda4ece41aac49b7b7ff8ddb55a7fe08
# bad: [b3c34245756adada8a50bdaedbb3965b071c7b0a] kasan: catch invalid free before SLUB reinitializes the object
git bisect bad b3c34245756adada8a50bdaedbb3965b071c7b0a
# good: [2eb14c1c2717396f2fb1e4a4c5a1ec87cdd174f6] mm, slab: reintroduce rcu_barrier() into kmem_cache_destroy()
git bisect good 2eb14c1c2717396f2fb1e4a4c5a1ec87cdd174f6
# good: [6c6c47b063b593785202be158e61fe5c827d6677] mm, slab: call kvfree_rcu_barrier() from kmem_cache_destroy()
git bisect good 6c6c47b063b593785202be158e61fe5c827d6677
# bad: [4e1c44b3db79ba910adec32e2e1b920a0e34890a] kunit, slub: add test_kfree_rcu() and test_leak_destroy()
git bisect bad 4e1c44b3db79ba910adec32e2e1b920a0e34890a
# first bad commit: [4e1c44b3db79ba910adec32e2e1b920a0e34890a] kunit, slub: add test_kfree_rcu() and test_leak_destroy()