Subject: Re: [BUG -next] "memcg: charge before adding to swapcache on swapin" broken

From: Heiko Carstens <[email-masked]>
Date: Wed, 17 Mar 2021 21:44:21 +0100

On Wed, Mar 17, 2021 at 08:44:14AM -0700, Shakeel Butt wrote:
> > Config below. And the fun thing is that I cannot reproduce it today
> > anymore with the elfutils test case - what _seems_ to be different is
> > that the test suite runs much faster than yesterday evening. Usually
> > an indication that there is no steal time (other guests which steal
> > cpu time), which again _could_ indicate a race / lack of locking
> > somewhere.
> > This is kind of odd, since yesterday evening it was very reliable to
> > trigger the bug :/
> >
> 
> Thanks for the config. One question regarding swap, is it disk based
> swap or zram?

Swap device is a real disk.

> By guests, do you mean there was another significant workload running
> on the machine in parallel to the tests?

That I don't know. I didn't check. I still can't reproduce with
elfutils anymore, however...

> If you don't mind can you try swapping01 as well.

ltp's swapping01 test triggers immediately random processes being
killed with SIGSEGV. I also tested with linux-next 20210316 and _only_
"memcg: charge before adding to swapcache on swapin" being reverted on
top, and the problem is away - so it looks like the result of
yesterday's bisect is indeed valid.