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

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Message-ID: <CALzav=fcN17cxdKseGAGHveTVYZNJwbEL6za6+DbKp-uiZwaOg@mail.gmail.com>
Date: Mon, 26 Jan 2026 11:46:27 -0800
From: David Matlack <dmatlack@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>, Michael Jeanson <mjeanson@...icios.com>, 
	Jens Axboe <axboe@...nel.dk>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	Peter Zijlstra <peterz@...radead.org>, "Paul E. McKenney" <paulmck@...nel.org>, X86 ML <x86@...nel.org>, 
	Sean Christopherson <seanjc@...gle.com>, Wei Liu <wei.liu@...nel.org>
Subject: SIGSEGVs after 39a167560a61 ("rseq: Optimize event setting")

Hi Thomas,

I started seeing SIGSEGVs in Google's remote test executor when
running on hosts at v6.19-rc6. Bisecting led me to this commit:

  39a167560a61 ("rseq: Optimize event setting")

I discovered this issue while running VFIO selftests against v6.19-rc6,
but realized the issue has nothing to do with the selftests themselves.
Even running "sleep" as the test is enough to trigger this issue in the
executor.

I know that Google uses rseq in its userspace software stack, so I
assume this is some bad interaction between that implementation and
commit 39a167560a61.

Unfortunately, the remote test executor that is receiving the SIGSEGV is
not open source so I don't have a repro I can share. But I can easily
reproduce the issue with my setup so I'd be happy to help with testing
any fixes or debug patches.

I've attached the .config that I used when reproducing this issue. The
host I am using is an Intel server with EMR CPUs in case that matters.

Thanks for the help.
--David

View attachment "config.txt" of type "text/plain" (170697 bytes)