Re: [PATCH slab hotfixes v2 2/2] slub/kunit: skip test_kfree_rcu when the slub kunit test is built-in

[Vlastimil Babka <vbabka@suse.cz>]

On 10/1/24 18:20, Vlastimil Babka wrote:
> Guenter Roeck reports that the new slub kunit tests added by commit
> 4e1c44b3db79 ("kunit, slub: add test_kfree_rcu() and
> test_leak_destroy()") cause a lockup on boot on several architectures
> when the kunit tests are configured to be built-in and not modules.
> 
> The test_kfree_rcu test invokes kfree_rcu() and boot sequence inspection
> showed the runner for built-in kunit tests kunit_run_all_tests() is
> called before setting system_state to SYSTEM_RUNNING and calling
> rcu_end_inkernel_boot(), so this seems like a likely cause. So while I
> was unable to reproduce the problem myself, skipping the test when the
> slub_kunit module is built-in should avoid the issue.
> 
> An alternative fix that was moving the call to kunit_run_all_tests() a
> bit later in the boot was tried, but has broken tests with functions
> marked as __init due to free_initmem() already being done.
> 
> Fixes: 4e1c44b3db79 ("kunit, slub: add test_kfree_rcu() and test_leak_destroy()")
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Closes: https://lore.kernel.org/all/6fcb1252-7990-4f0d-8027-5e83f0fb9409@roeck-us.net/

I hope you can confirm it helps, because the commit added two tests and I've
only skipped one of them, as it's the one using kfree_rcu(), which is
suspected. But the other is responsible for the (now suppressed)
kmem_cache_destroy() warning, and maybe I'm missing something and it was
actually that one causing the lockups.

Since you mentioned the boot lockups happened on some x86_64 too, do you
have a .config of the lockup case? I've tried tweaking some rcu options but
still nothing.

Thanks!

> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Boqun Feng <boqun.feng@gmail.com>
> Cc: Uladzislau Rezki <urezki@gmail.com>
> Cc: rcu@vger.kernel.org
> Cc: Brendan Higgins <brendanhiggins@google.com>
> Cc: David Gow <davidgow@google.com>
> Cc: Rae Moar <rmoar@google.com>
> Cc: linux-kselftest@vger.kernel.org
> Cc: kunit-dev@googlegroups.com
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>  lib/slub_kunit.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/slub_kunit.c b/lib/slub_kunit.c
> index 85d51ec09846d4fa219db6bda336c6f0b89e98e4..80e39f003344858722a544ad62ed84e885574054 100644
> --- a/lib/slub_kunit.c
> +++ b/lib/slub_kunit.c
> @@ -164,10 +164,16 @@ struct test_kfree_rcu_struct {
>  
>  static void test_kfree_rcu(struct kunit *test)
>  {
> -	struct kmem_cache *s = test_kmem_cache_create("TestSlub_kfree_rcu",
> -				sizeof(struct test_kfree_rcu_struct),
> -				SLAB_NO_MERGE);
> -	struct test_kfree_rcu_struct *p = kmem_cache_alloc(s, GFP_KERNEL);
> +	struct kmem_cache *s;
> +	struct test_kfree_rcu_struct *p;
> +
> +	if (IS_BUILTIN(CONFIG_SLUB_KUNIT_TEST))
> +		kunit_skip(test, "can't do kfree_rcu() when test is built-in");
> +
> +	s = test_kmem_cache_create("TestSlub_kfree_rcu",
> +				   sizeof(struct test_kfree_rcu_struct),
> +				   SLAB_NO_MERGE);
> +	p = kmem_cache_alloc(s, GFP_KERNEL);
>  
>  	kfree_rcu(p, rcu);
>  	kmem_cache_destroy(s);
>