Re: mm: LTP/memcg testcase regression induced by 8cd7c588decf..66ce520bb7c2 series

Re: mm: LTP/memcg testcase regression induced by 8cd7c588decf..66ce520bb7c2 series

[Thorsten Leemhuis]

Hi, this is your Linux kernel regression tracker speaking.

CCing regression mailing list, which should be in the loop for all
regressions, as explained here:
https://www.kernel.org/doc/html/latest/admin-guide/reporting-issues.html

On 21.11.21 11:57, Mike Galbraith wrote:
> Greetings,
> 
> FYI, something in this series causes LTP controllers::memcg_regression
> testcase to hang forever.  Verified via brute force revert of the lot.
> 
> After letting box moan for 4.5 hours, I poked ^C repeatedly, but runltp
> didn't exit/recover gracefully, and ps hung, so I nuked the box.  All
> memcg_test_1 instances were stuck in reclaim_throttle().
> [...]

TWIMC: To be sure this issue doesn't fall through the cracks unnoticed,
I'm adding it to regzbot, my Linux kernel regression tracking bot:

#regzbot ^introduced 8cd7c588decf..66ce520bb7c2
#regzbot ignore-activity

Ciao, Thorsten, your Linux kernel regression tracker.

P.S.: If you want to know more about regzbot, check out its
web-interface, the getting start guide, and/or the references documentation:

https://linux-regtracking.leemhuis.info/regzbot/
https://gitlab.com/knurd42/regzbot/-/blob/main/docs/getting_started.md
https://gitlab.com/knurd42/regzbot/-/blob/main/docs/reference.md

The last two documents will explain how you can interact with regzbot
yourself if your want to.

Hint for the reporter: when reporting a regression it's in your interest
to tell #regzbot about it in the report, as that will ensure the
regression gets on the radar of regzbot and the regression tracker.
That's in your interest, as they will make sure the report won't fall
through the cracks unnoticed.

Hint for developers: you normally don't need to care about regzbot, just
fix the issue as you normally would. Just remember to include a 'Link:'
tag to the report in the commit message, as explained in
Documentation/process/submitting-patches.rst
That aspect was recently was made more explicit in commit 1f57bd42b77c:
https://git.kernel.org/linus/1f57bd42b77c


P.P.S.: As a Linux kernel regression tracker I'm getting a lot of
reports on my table. I can only look briefly into most of them.
Unfortunately therefore I sometimes will get things wrong or miss
something important. I hope that's not the case here; if you think it
is, don't hesitate to tell me about it in a public reply. That's in
everyone's interest, as what I wrote above might be misleading to
everyone reading this; any suggestion I gave they thus might sent
someone reading this down the wrong rabbit hole, which none of us wants.

BTW, I have no personal interest in this issue, which is tracked using
regzbot, my Linux kernel regression tracking bot
(https://linux-regtracking.leemhuis.info/regzbot/). I'm only posting
this mail to get things rolling again and hence don't need to be CC on
all further activity wrt to this regression.

Re: mm: LTP/memcg testcase regression induced by 8cd7c588decf..66ce520bb7c2 series

[Mike Galbraith]

On Sun, 2021-11-21 at 14:51 +0100, Thorsten Leemhuis wrote:
>
> Hi, this is your Linux kernel regression tracker speaking.

This isn't necessarily a kernel regression, though the fact that
bystander tasks like ps can get snagged for ages as the testcase runs
at an amazingly glacial pace doesn't look particularly wonderful.

homer:/root # time ps lax
...
real    11m33.258s
user    0m0.004s
sys     0m0.008s
homer:/root #

The other memcg tests complete fine, though taking more time to do so.
Running all tests except memcg_regression, (and  memcg_stress because
it's a 30 minute swap storm from hell as delivered), runtime increased
from 0m37s to 4m43s.

The problematic testcase is root intentionally shooting its own foot,
then checking for battle damage that occurred in days of yore, so it
now hurting in a different way isn't necessarily grounds to gripe at
the kernel.. even with the rather ugly side effects.. maybe <shrug>.

#---------------------------------------------------------------------------
# Bug:    The bug was, while forking mass processes, trigger memcgroup OOM,
#         then NULL pointer dereference may be hit.
# Kernel: 2.6.25-rcX
# Links:  http://lkml.org/lkml/2008/4/14/38
# Fix:    commit e115f2d89253490fb2dbf304b627f8d908df26f1
#---------------------------------------------------------------------------
test_1()
{
        mkdir memcg/0/
        echo 0 > memcg/0/memory.limit_in_bytes

        ./memcg_test_1

        rmdir memcg/0/

        check_kernel_bug
        if [ $? -eq 1 ]; then
                tst_resm TPASS "no kernel bug was found"
        fi
}


I'm gonna just comment the little bugger out as obsolete and walk away.

	-Mike

Re: mm: LTP/memcg testcase regression induced by 8cd7c588decf..66ce520bb7c2 series

[Mike Galbraith]

On Mon, 2021-11-22 at 07:46 +0100, Mike Galbraith wrote:
> 
> #--------------------------------------------------------------------
> -------
> # Bug:    The bug was, while forking mass processes, trigger
> memcgroup OOM,
> #         then NULL pointer dereference may be hit.
> # Kernel: 2.6.25-rcX
> # Links:  http://lkml.org/lkml/2008/4/14/38
> # Fix:    commit e115f2d89253490fb2dbf304b627f8d908df26f1
> #--------------------------------------------------------------------
> -------
> test_1()
> {       
>         mkdir memcg/0/
>         echo 0 > memcg/0/memory.limit_in_bytes
>         
>         ./memcg_test_1
>         
>         rmdir memcg/0/
>         
>         check_kernel_bug 
>         if [ $? -eq 1 ]; then
>                 tst_resm TPASS "no kernel bug was found"
>         fi
> }
> 
> 
> I'm gonna just comment the little bugger out as obsolete and walk
> away.

test2() and test3() then pass, but test_4() hangs, and looks like it
should not, so...

	-Mike

Re: mm: LTP/memcg testcase regression induced by 8cd7c588decf..66ce520bb7c2 series #justforregzbot

[Thorsten Leemhuis]

On 21.11.21 14:51, Thorsten Leemhuis wrote:
> On 21.11.21 11:57, Mike Galbraith wrote:
>> Greetings,
>>
>> FYI, something in this series causes LTP controllers::memcg_regression
>> testcase to hang forever.  Verified via brute force revert of the lot.
>>
>> After letting box moan for 4.5 hours, I poked ^C repeatedly, but runltp
>> didn't exit/recover gracefully, and ps hung, so I nuked the box.  All
>> memcg_test_1 instances were stuck in reclaim_throttle().
>> [...]
> 
> TWIMC: To be sure this issue doesn't fall through the cracks unnoticed,
> I'm adding it to regzbot, my Linux kernel regression tracking bot:
> 
> #regzbot ^introduced 8cd7c588decf..66ce520bb7c2
> #regzbot ignore-activity

#regzbot link:
https://lore.kernel.org/lkml/20211124011954.7cab9bb4@mail.inbox.lv/
Related regression, likely to be fixed by the same patch