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

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Message-ID: <199b8846-40c3-4307-8fd5-c93b59268dc4@efficios.com>
Date: Mon, 26 Jan 2026 17:35:18 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: David Matlack <dmatlack@...gle.com>, Thomas Gleixner <tglx@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, LKML
 <linux-kernel@...r.kernel.org>, Michael Jeanson <mjeanson@...icios.com>,
 Jens Axboe <axboe@...nel.dk>, "Paul E. McKenney" <paulmck@...nel.org>,
 X86 ML <x86@...nel.org>, Sean Christopherson <seanjc@...gle.com>,
 Wei Liu <wei.liu@...nel.org>
Subject: Re: SIGSEGVs after 39a167560a61 ("rseq: Optimize event setting")

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