Re: Observed recent memory leak in __anon_vma_prepare

[Liam Howlett <liam.howlett@oracle.com>]

* Lukas Bulwahn <lukas.bulwahn@gmail.com> [221011 12:35]:
> Dear Liam, dear Matthew, dear all,
> 
> The reproducer for the 'memory leak in __anon_vma_prepare' bug (see
> https://elisa-builder-00.iol.unh.edu/syzkaller-next/report?id=3113810b9abd3dfeb581759df93d3171d1a90f18)
> is reproducible, it is triggering the memory leak on the current
> mainline (commit 60bb8154d1d7), and it was not triggering on v6.0. My
> build config is a x86_64 defconfig.
> 
> My git bisection showed that:
> 
> 524e00b36e8c547f5582eef3fb645a8d9fc5e3df is the first bad commit
> commit 524e00b36e8c547f5582eef3fb645a8d9fc5e3df
> Author: Liam R. Howlett <Liam.Howlett@Oracle.com>
> Date:   Tue Sep 6 19:48:48 2022 +0000
> 
> The git bisect log is below, note that the commits 7fdbd37da5c6,
> d0cf3dd47f0d and 0c563f148043 are marked good in the git bisect as
> they caused bugs "BUG: Bad rss-counter state mm: ... type:MM_ANONPAGES
> val:2". This bug report might have overshadowed the actual issue, and
> hence the bug might have been introduced earlier, but was only visible
> once the Bad rss-counter state bug disappeared.
> 
> 

...

> # first bad commit: [524e00b36e8c547f5582eef3fb645a8d9fc5e3df] mm:
> remove rb tree.
> 
> 
> If there is more information needed or other bisection to be done,
> please let me know.


Lukas,

Thanks for the report.  I am trying to reproduce this issue and have not
been able to trigger a memory leak.  So far I have built using the
defconfig from arch/x86/configs/x86_64_defconfig and run the C code from
the end of your report above.  It also produces some output that is not
captured in your report.  Are you sure it's the defconfig being used?

------
# ./repro
write to /proc/sys/kernel/hung_task_check_interval_secs failed: No such
file or directory
write to /proc/sys/net/core/bpf_jit_kallsyms failed: No such file or
directory
write to /proc/sys/net/core/bpf_jit_harden failed: No such file or
directory
write to /proc/sys/kernel/softlockup_all_cpu_backtrace failed: No such
file or directory
------

Note your output does not mention softlockup or hung_task issues.  This
is on 6.0.0-rc3-00207-g524e00b36e8c.  It is also worth noting that the
resulting kernel does not have /sys/kernel/debug/kmemleak.

I have also tested your reproducer with my own config which does have
the kmemleak debug file, but it did not trigger a memory leak either.  I
suspect I am missing a config option?  Are you using gcc or clang?

Thanks,
Liam