linux-next: test failure after merge of the mm-nonmm-unstable tree

linux-next: test failure after merge of the mm-nonmm-unstable tree

[Mark Brown]

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Hi all,

After merging the mm-nonmm-unstable tree, today's linux-next testing
(arm64 kunit) failed like this:

$ qemu-system-aarch64 -nodefaults -m 1024 -kernel /tmp/next/arm64_kunit/arch/arm64/boot/Image.gz -append 'kunit.enable=1 console=ttyAMA0 kunit_shutdown=reboot' -no-reboot -nographic -accel kvm -accel hvf -accel tcg -serial stdio -machine virt -cpu max
[11:39:24] ============================================================
[11:39:24] ======== smp-cond-load-relaxed-timeout (3 subtests) ========
[11:39:24] # smp_cond_relaxed_timeout_succeeds: EXPECTATION FAILED at lib/tests/barrier-timeout-test.c:69
[11:39:24] Expected runtime <= timeout_ns == succeeds, but
[11:39:24]     runtime <= timeout_ns == 0 (0x0)
[11:39:24]     succeeds == 1 (0x1)
[11:39:24] [FAILED] smp_cond_relaxed_timeout_succeeds
[11:39:24]     # module: barrier_timeout_test
[11:39:24] # smp-cond-load-relaxed-timeout: pass:2 fail:1 skip:0 total:3
[11:39:24] # Totals: pass:2 fail:1 skip:0 total:3
[11:39:24] ========== [FAILED] smp-cond-load-relaxed-timeout ==========
[11:39:24] ============================================================
[11:39:24] Testing complete. Ran 9436 tests: passed: 9315, failed: 1, skipped: 120
[11:39:24] Failures: smp-cond-load-relaxed-timeout.smp_cond_relaxed_timeout_succeeds
[11:39:24] Test results stored in /tmp/next/arm64_kunit.json
[11:39:24] Elapsed time: 121.367s total, 0.002s configuring, 63.737s building, 57.613s running

Note that we are running on an arm64 host with access to KVM so the
above should be running with KVM rather than being emulated.

Caused by commit

   0403c34571d1d (kunit: add tests for smp_cond_load_relaxed_timeout())

in that it's adding the new test which fails, I didn't investigate the
quality of the test.  I do note that there's some related functional
work also from Ankur that's also added by the mm-nonmm-unstable tree but
didn't investigate that either.

I have used the version from next-20260506 instead, the code was in
next-20260508 but I belive Thierry was emulating.

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Re: linux-next: test failure after merge of the mm-nonmm-unstable tree

[Mark Brown]

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On Mon, May 18, 2026 at 01:00:07PM +0100, Mark Brown wrote:

> After merging the mm-nonmm-unstable tree, today's linux-next testing
> (arm64 kunit) failed like this:

> [11:39:24] Failures: smp-cond-load-relaxed-timeout.smp_cond_relaxed_timeout_succeeds

> Note that we are running on an arm64 host with access to KVM so the
> above should be running with KVM rather than being emulated.

> Caused by commit

>    0403c34571d1d (kunit: add tests for smp_cond_load_relaxed_timeout())

> in that it's adding the new test which fails, I didn't investigate the
> quality of the test.  I do note that there's some related functional
> work also from Ankur that's also added by the mm-nonmm-unstable tree but
> didn't investigate that either.

> I have used the version from next-20260506 instead, the code was in
> next-20260508 but I belive Thierry was emulating.

Actually these patches were introduced in next-20260427 so I'll need to
go back to next-20260424 instead, sorry (got confused by the tree
rebasing).  It looks like something in the more recent versions made the
issue more promienent.

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Re: linux-next: test failure after merge of the mm-nonmm-unstable tree

[Ankur Arora]

Mark Brown <broonie@kernel.org> writes:

> On Mon, May 18, 2026 at 01:00:07PM +0100, Mark Brown wrote:
>
>> After merging the mm-nonmm-unstable tree, today's linux-next testing
>> (arm64 kunit) failed like this:
>
>> [11:39:24] Failures: smp-cond-load-relaxed-timeout.smp_cond_relaxed_timeout_succeeds
>
>> Note that we are running on an arm64 host with access to KVM so the
>> above should be running with KVM rather than being emulated.
>
>> Caused by commit
>
>>    0403c34571d1d (kunit: add tests for smp_cond_load_relaxed_timeout())
>
>> in that it's adding the new test which fails, I didn't investigate the
>> quality of the test.  I do note that there's some related functional
>> work also from Ankur that's also added by the mm-nonmm-unstable tree but
>> didn't investigate that either.
>
>> I have used the version from next-20260506 instead, the code was in
>> next-20260508 but I belive Thierry was emulating.
>
> Actually these patches were introduced in next-20260427 so I'll need to
> go back to next-20260424 instead, sorry (got confused by the tree
> rebasing).  It looks like something in the more recent versions made the
> issue more promienent.

Hi Mark

Thanks for the report. The failing test case is using a kthread to
toggle a bit which the test depends on.

The first test condition succeeds:

  KUNIT_EXPECT_EQ(test, (bool)(result & TEST_FLAG_VAL), succeeds)

so the bit did get toggled. The second condition (runtime <= timeout_ns)
failed:

  KUNIT_EXPECT_EQ(test, runtime <= timeout_ns, succeeds)

Possibly because the we got scheduled out while running the test. Not
sure why the test started failing now. I'm guessing the VM running the
test isn't under CPU stress and the like.

If that can happen then I should relax the second condition.

--
ankur

Re: linux-next: test failure after merge of the mm-nonmm-unstable tree

[Ankur Arora]

Ankur Arora <ankur.a.arora@oracle.com> writes:

> Mark Brown <broonie@kernel.org> writes:
>
>> On Mon, May 18, 2026 at 01:00:07PM +0100, Mark Brown wrote:
>>
>>> After merging the mm-nonmm-unstable tree, today's linux-next testing
>>> (arm64 kunit) failed like this:
>>
>>> [11:39:24] Failures: smp-cond-load-relaxed-timeout.smp_cond_relaxed_timeout_succeeds
>>
>>> Note that we are running on an arm64 host with access to KVM so the
>>> above should be running with KVM rather than being emulated.
>>
>>> Caused by commit
>>
>>>    0403c34571d1d (kunit: add tests for smp_cond_load_relaxed_timeout())
>>
>>> in that it's adding the new test which fails, I didn't investigate the
>>> quality of the test.  I do note that there's some related functional
>>> work also from Ankur that's also added by the mm-nonmm-unstable tree but
>>> didn't investigate that either.
>>
>>> I have used the version from next-20260506 instead, the code was in
>>> next-20260508 but I belive Thierry was emulating.
>>
>> Actually these patches were introduced in next-20260427 so I'll need to
>> go back to next-20260424 instead, sorry (got confused by the tree
>> rebasing).  It looks like something in the more recent versions made the
>> issue more promienent.
>
> Hi Mark
>
> Thanks for the report. The failing test case is using a kthread to
> toggle a bit which the test depends on.
>
> The first test condition succeeds:
>
>   KUNIT_EXPECT_EQ(test, (bool)(result & TEST_FLAG_VAL), succeeds)
>
> so the bit did get toggled. The second condition (runtime <= timeout_ns)
> failed:
>
>   KUNIT_EXPECT_EQ(test, runtime <= timeout_ns, succeeds)
>
> Possibly because the we got scheduled out while running the test. Not
> sure why the test started failing now. I'm guessing the VM running the
> test isn't under CPU stress and the like.
>
> If that can happen then I should relax the second condition.

Thinking some more, the condition is much too strict.

Instead of:
  succeeds => (runtime <= timeout_ns)

A better check would be:
  !succeeds => runtime >= timeout_ns

I'll send a patch to that effect.

Thanks

--
ankur

Re: linux-next: test failure after merge of the mm-nonmm-unstable tree

[Mark Brown]

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On Mon, May 18, 2026 at 11:02:30PM -0700, Ankur Arora wrote:
> Ankur Arora <ankur.a.arora@oracle.com> writes:
> > Mark Brown <broonie@kernel.org> writes:

> >>> Note that we are running on an arm64 host with access to KVM so the
> >>> above should be running with KVM rather than being emulated.

> > Possibly because the we got scheduled out while running the test. Not
> > sure why the test started failing now. I'm guessing the VM running the
> > test isn't under CPU stress and the like.

Yes, the system should be doing nothing except run KUnit and any random
background stuff, it's pretty high end so any background stuff shouldn't
need to disturb KUnit.  At some point I will go back to running multiple
tests in parallel but didn't do that yet.

As I indicated above I'm fairly sure the main difference is that I'm
running on actual hardware not emulation, though I do think there's
something else that made it more prominent in that situation.  I'm
fairly sure Thierry was using emulation while he was running -next.

> > If that can happen then I should relax the second condition.

> Thinking some more, the condition is much too strict.

> Instead of:
>   succeeds => (runtime <= timeout_ns)

> A better check would be:
>   !succeeds => runtime >= timeout_ns

> I'll send a patch to that effect.

Hopefully that's it...

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