Re: hunting memory corruption bug in 6.18.x

[Andrew Morton]

On Mon, 19 Oct 2026 17:22:37 +0200 Nikola Ciprich <nikola.ciprich@xxxxxxxxxxx> wrote:

> > 
> > Sure! And I have more good news: after applying 55780d8a1dcc
> > to 6.18.56, I was able to perform more than 30 migrations without
> > a glitch. After booting back into 6.18.56 without it, both VMs
> > crashed within 2-3 migrations. Furthermore, some memory apparently
> > got corrupted on one of the hosts, since various commands started
> > crashing too:
> > 
> > [  303.466091] traps: systemd-logind[3085] trap invalid opcode ip:7f7b5667e616 sp:7ffe1afdec38 error:0 in libsystemd-shared-252.so[7e616,7f7b5666d000+22e000]
> > [  303.493810] traps: systemd-coredum[11269] trap invalid opcode ip:7fc6bf67f614 sp:7ffc075da958 error:0 in libsystemd-shared-252.so[7f614,7fc6bf66d000+22e000]
> > [  377.528955] traps: systemd[5607] trap invalid opcode ip:7f791447e616 sp:7ffe83e61cf8 error:0 in libsystemd-shared-252.so[7e616,7f791446d000+22e000]
> > [  377.556993] traps: systemd-coredum[12080] trap invalid opcode ip:7f97ce07f614 sp:7ffe28b56a88 error:0 in libsystemd-shared-252.so[7f614,7f97ce06d000+22e000]
> > [ 3746.173043] traps: hostnamectl[45846] trap invalid opcode ip:7fe00cc7f614 sp:7fff89916e48 error:0 in libsystemd-shared-252.so[7f614,7fe00cc6d000+22e000]
> > [ 3746.202305] traps: systemd-coredum[45847] trap invalid opcode ip:7f7fe9e7f614 sp:7ffea227cfa8 error:0 in libsystemd-shared-252.so[7f614,7f7fe9e6d000+22e000]
> > [ 3750.581940] traps: systemctl[45903] trap invalid opcode ip:7fbb8967f614 sp:7fff733e5748 error:0 in libsystemd-shared-252.so[7f614,7fbb8966d000+22e000]
> > [ 3750.612651] traps: systemd-coredum[45904] trap invalid opcode ip:7f90d347f614 sp:7ffdc7f55148 error:0 in libsystemd-shared-252.so[7f614,7f90d346d000+22e000]
> > 
> > I'm not sure if this is of any use, but I collected a vmcore of
> > this state by intentionally crashing the host via /proc/sysrq-trigger.
> > 
> > Anyway, I'll give 55780d8a1dcc some more migration rounds, but it looks
> > promising.
> 
> 500+ migrations back and forth, no issues. I consider this solved and am rolling
> out the patched kernel; I’ll report if anything new turns up.

Great, thanks.

oops, we haven't been cc'ing Yosry.

> Definitely a -stable candidate. Andrew, will you send it to Greg, or shall I?

I volunteer Yosry or Sean ;)

I think 55780d8a1dcc should be repackaged before sending over to the
-stable people.  Its changelog is very wrong: "The bug is benign
though".  Update the changelog to explain that the bug is in fact evil.
Otherwise -stable and further downstream won't understand why we sent
it to them and won't understand the impact.

And that repackaging would be an opportunity to add
Reported-by:/Closes:/Tested-by: you, which is the least we can do to
thank you for all this diligent work!