Re: [PATCH slab hotfixes 2/2] kunit: move call to kunit_run_all_tests() after rcu_end_inkernel_boot()

[Vlastimil Babka]

On 10/1/24 1:55 AM, Guenter Roeck wrote:
> On 9/30/24 11:50, Guenter Roeck wrote:
>> On 9/30/24 01:37, 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.
>>>
>>> These tests invoke kfree_rcu() and kvfree_rcu_barrier() 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,
>>> moving the call to kunit_run_all_tests() a bit later in the boot seems
>>> to have fixed the lockup problem according to Guenter's limited testing.
>>>
>>> No kunit tests should be broken by calling the built-in executor a bit
>>> later, as when compiled as modules, they are still executed even later
>>> than this.
>>>
> 
> Actually, that is wrong.
> 
> Turns out kunit_iov_iter (and other kunit tests) are marked __init.
> That means those unit tests have to run before the init code is released,
> and it actually _is_ harmful to run the tests after rcu_end_inkernel_boot()
> because at that time free_initmem() has already been called.

Oh, guess that explains why the kunit_run_all_tests() executor is called
so suspiciously early. Of course when built as modules, __init has a
different lifetime.

Guess I will just skip the two new tests using kfree_rcu() when the slub
kunit is built-in then. Thanks for testing.

> Guenter
> 
>>> Fixes: 4e1c44b3db79 ("kunit, slub: add test_kfree_rcu() and
>>> test_leak_destroy()")
>>> Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
>>> Closes:
>>> https://lore.kernel.org/all/6fcb1252-7990-4f0d-8027-5e83f0fb9409@xxxxxxxxxxxx/
>>> Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
>>> Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
>>> Cc: Uladzislau Rezki <urezki@xxxxxxxxx>
>>> Cc: rcu@xxxxxxxxxxxxxxx
>>> Cc: Brendan Higgins <brendanhiggins@xxxxxxxxxx>
>>> Cc: David Gow <davidgow@xxxxxxxxxx>
>>> Cc: Rae Moar <rmoar@xxxxxxxxxx>
>>> Cc: linux-kselftest@xxxxxxxxxxxxxxx
>>> Cc: kunit-dev@xxxxxxxxxxxxxxxx
>>> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
>>> ---
>>>   init/main.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/init/main.c b/init/main.c
>>> index
>>> c4778edae7972f512d5eefe8400075ac35a70d1c..7890ebb00e84b8bd7bac28923fb1fe571b3e9ee2 100644
>>> --- a/init/main.c
>>> +++ b/init/main.c
>>> @@ -1489,6 +1489,8 @@ static int __ref kernel_init(void *unused)
>>>       rcu_end_inkernel_boot();
>>> +    kunit_run_all_tests();
>>> +
>>>       do_sysctl_args();
>>>       if (ramdisk_execute_command) {
>>> @@ -1579,8 +1581,6 @@ static noinline void __init
>>> kernel_init_freeable(void)
>>>       do_basic_setup();
>>> -    kunit_run_all_tests();
>>> -
>>>       wait_for_initramfs();
>>>       console_on_rootfs();
>>>
>> Unfortunately it doesn't work. With this patch applied, I get many
>> backtraces
>> similar to the following, and ultimately the image crashes. This is
>> with arm64.
>> I do not see the problem if I drop this patch.
>>
>> Guenter
>>
>> ---
>> [    9.465871]     KTAP version 1
>> [    9.465964]     # Subtest: iov_iter
>> [    9.466056]     # module: kunit_iov_iter
>> [    9.466115]     1..12
>> [    9.467000] Unable to handle kernel paging request at virtual
>> address ffffc37db5c9f26c
>> [    9.467244] Mem abort info:
>> [    9.467332]   ESR = 0x0000000086000007
>> [    9.467454]   EC = 0x21: IABT (current EL), IL = 32 bits
>> [    9.467576]   SET = 0, FnV = 0
>> [    9.467667]   EA = 0, S1PTW = 0
>> [    9.467762]   FSC = 0x07: level 3 translation fault
>> [    9.467912] swapper pgtable: 4k pages, 48-bit VAs,
>> pgdp=0000000042a59000
>> [    9.468055] [ffffc37db5c9f26c] pgd=0000000000000000,
>> p4d=1000000044b36003, pud=1000000044b37003, pmd=1000000044b3a003,
>> pte=0000000000000000
>> [    9.469430] Internal error: Oops: 0000000086000007 [#1] PREEMPT SMP
>> [    9.469687] Modules linked in:
>> [    9.470035] CPU: 0 UID: 0 PID: 550 Comm: kunit_try_catch Tainted:
>> G                 N 6.12.0-rc1-00005-ga65e3eb58cdb #1
>> [    9.470290] Tainted: [N]=TEST
>> [    9.470356] Hardware name: linux,dummy-virt (DT)
>> [    9.470530] pstate: 80000005 (Nzcv daif -PAN -UAO -TCO -DIT -SSBS
>> BTYPE=--)
>> [    9.470656] pc : iov_kunit_copy_to_kvec+0x0/0x334
>> [    9.471055] lr : kunit_try_run_case+0x6c/0x15c
>> [    9.471145] sp : ffff800080883de0
>> [    9.471210] x29: ffff800080883e20 x28: 0000000000000000 x27:
>> 0000000000000000
>> [    9.471376] x26: 0000000000000000 x25: 0000000000000000 x24:
>> ffff80008000bb68
>> [    9.471501] x23: ffffc37db3f7093c x22: ffff80008000b940 x21:
>> ffff545847af4c00
>> [    9.471622] x20: ffff545847cd3940 x19: ffff80008000bb50 x18:
>> 0000000000000006
>> [    9.471742] x17: 6c61746f7420303a x16: 70696b7320303a6c x15:
>> 0000000000000172
>> [    9.471863] x14: 0000000000020000 x13: 0000000000000000 x12:
>> ffffc37db6a600c8
>> [    9.471983] x11: 0000000000000043 x10: 0000000000000043 x9 :
>> 1fffffffffffffff
>> [    9.472122] x8 : 00000000ffffffff x7 : 000000001040d4fd x6 :
>> ffffc37db70c3810
>> [    9.472243] x5 : 0000000000000000 x4 : ffffffffc4653600 x3 :
>> 000000003b9ac9ff
>> [    9.472363] x2 : 0000000000000001 x1 : ffffc37db5c9f26c x0 :
>> ffff80008000bb50
>> [    9.472572] Call trace:
>> [    9.472636]  iov_kunit_copy_to_kvec+0x0/0x334
>> [    9.472740]  kunit_generic_run_threadfn_adapter+0x28/0x4c
>> [    9.472835]  kthread+0x11c/0x120
>> [    9.472903]  ret_from_fork+0x10/0x20
>> [    9.473146] Code: ???????? ???????? ???????? ???????? (????????)
>> [    9.473505] ---[ end trace 0000000000000000 ]---
>>
>