From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 50A1D2D5923 for ; Mon, 26 Jan 2026 20:47:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769460475; cv=none; b=uoHqCYVNiFxmdQ/g1f+XljOIPRwkNQcjYuJsVIzArnwm5ZdzD8nX1k9Acsw2BG3lPbV7VYSwWxyMrQW2Yi7uzMMtery2TrDnklcnuot/zjmVs864iQi8MXCZNKAj4EWxG2askUPl4DORJPUSFbM1C7jwep2Ra+8ZkxqTuo9wWQk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769460475; c=relaxed/simple; bh=CJ8aXqTCRkP2QYMX1iAXhzrODUPNv3tUjHnzMxVIckk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Sis80/hbFa7LKf53EI9hIVkY68XcnkWTyqF9BHSDP1IeO1V7KJtdxXqZ5tejOnpKsD+eILtwFXBI6yHJEvzxmCziWKlubqyo8SJP/4d9n8KKOshwv3NHSii2VdEmh9ocDTJRqkkFes4Tkj/FC7YKP91h4xz1+Xy51bAWBDZR/Zg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=in+ZaHpC; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="in+ZaHpC" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=j1MnoWW1uSn7AA+GjretJCZNca0gsFdEWtEquuCdjT8=; b=in+ZaHpC0qZu9vAGckKOIDeDgT +c0aODazWv7msDRwtMXO/bJFbwt+bj1CapR59PEt8FQ6GfmyiGE9yjQWmFwOxdhVVQg/1I/7RYYo4 HzqryrtCKhG4eKokB8N17HHgfGa/HMuZRJ8TQKFQSxQ+FG7/vWbkEPfaZXOOyamrw1bblZNA/hy4N W6TUlvJGS3oAxtCh8sEFRFpXoMLYwDCxfT4sHVsPFZfCDQK92z1waWcM1dNmZ13eC1FJIFVz0n//2 qgvmWFmvZILbv/OEalcSGAhJUeNn3n4Vrj3q1eDVP2Jy0znLLPr8mmeKvVgwKy5/iub7JCosCSHrR pGXwZoGw==; Received: from 2001-1c00-8d85-5700-266e-96ff-fe07-7dcc.cable.dynamic.v6.ziggo.nl ([2001:1c00:8d85:5700:266e:96ff:fe07:7dcc] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vkTUx-00000005qpV-3qaw; Mon, 26 Jan 2026 20:47:48 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id E2D1C300756; Mon, 26 Jan 2026 21:47:45 +0100 (CET) Date: Mon, 26 Jan 2026 21:47:45 +0100 From: Peter Zijlstra To: David Matlack Cc: Thomas Gleixner , LKML , Michael Jeanson , Jens Axboe , Mathieu Desnoyers , "Paul E. McKenney" , X86 ML , Sean Christopherson , Wei Liu Subject: Re: SIGSEGVs after 39a167560a61 ("rseq: Optimize event setting") Message-ID: <20260126204745.GP171111@noisy.programming.kicks-ass.net> References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Jan 26, 2026 at 11:46:27AM -0800, David Matlack wrote: > 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. Is this using tcmalloc? If so, that is somewhat expected because tcmalloc is known to violate upstream rseq ABI. IIRC you should get a nice splat if you enable rseq debug mode (echo 1 > /debug/rseq/debug). Perhaps this is the nudge Google needs to go fix this.