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

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

+CC Dmitry and Marco.

On 2026-01-26 17:35, Mathieu Desnoyers wrote:
> On 2026-01-26 17:27, David Matlack wrote:
>> On Mon, Jan 26, 2026 at 1:51 PM Thomas Gleixner <tglx@kernel.org> 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