Re: SIGSEGVs after 39a167560a61 ("rseq: Optimize event setting")

[Mathieu Desnoyers]

On 2026-01-26 17:27, David Matlack wrote:
> On Mon, Jan 26, 2026 at 1:51 PM Thomas Gleixner <tglx@xxxxxxxxxx> wrote:
[...]
> > > Perhaps this is the nudge Google needs to go fix this.
> >
> > The real question is whether the segfault is triggered from the rseq
> > sanity checks or if the application segfaults becauses it relies on
> > something something which is not guaranteed by the ABI. As this is
> > secret sauce, I can't tell.
>
> I tried enabling /debug/rseq/debug but many of the daemons on my host
> started crash-looping so much that I wasn't able to even run my test.
>
> Next I tried disabling CONFIG_RSEQ and as expected the issue went
> away. I will use that for now to unblock my VFIO testing.
>
> I have reported the tcmalloc regression internally within Google to
> figure out what next step they want to take.

Note that I've proposed to help out the tcmalloc people a few
times in the past years to fix this, but I've been told that
it was not a priority on their end, and that they would not be
able to even test whatever I would come up with.

Thanks,

Mathieu

--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com