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

[David Gow <davidgow@google.com>]

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On Tue, 1 Oct 2024 at 07:55, Guenter Roeck <linux@roeck-us.net> 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.

Yeah: some tests are marked __init. KUnit does actually mark these
with an attribute, so we can potentially split the execution up into
an 'init' part which runs early, and a later part, but there are some
complications if we still want to track the total number of tests and
support filtering, etc. properly.

That's something I think we'll look at for 6.13: in the meantime,
skipping the problematic slub tests when built-in seems to be the
right short-term fix. I'll look into having the built-in executor
moved later for non-init tests once we've worked out how best to adapt
the filter/KTAP output code to do so as cleanly as possible.

Cheers,
-- David


>
> Guenter
>
> >> 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/
> >> 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>
> >> ---
> >>   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 ]---
> >
>

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