From nobody Mon Feb 9 11:07:34 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 506A5C77B7A for ; Wed, 7 Jun 2023 21:21:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231583AbjFGVVW (ORCPT ); Wed, 7 Jun 2023 17:21:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46066 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231935AbjFGVVU (ORCPT ); Wed, 7 Jun 2023 17:21:20 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1DABC1984; Wed, 7 Jun 2023 14:21:19 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id A6CEA6488A; Wed, 7 Jun 2023 21:21:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 85B6EC433D2; Wed, 7 Jun 2023 21:21:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686172878; bh=jSlEKrCnMK95pETVHXEKH30RppvMmXwHnRIAJknEjUM=; h=From:Date:Subject:To:Cc:From; b=gJdnOvtTm3qZwrlGnx/agmFkFlojWgz2nJIaWWcgj1exOo3F19P5F3ej0gTkJfLtK PH09tXlsjrcX23Fkor3z+4Oz9hYwzEwJ11TKAFLwh/hviAt4xrQiyg3tvOOUaA2odh ZY84y3mh4FY5sn+V1Hef3B1o7cd5ZwXvboL/EAdZq3xr+HX9fcD62fAE1hhKLpb6Tu HPZRLhfaOCCoqjIh+/vnApqwAvy/Jje4UxFHlyX/i/7ocueef60FvfYYkCNZJGU3b4 bewoMXcm6M28KgXLwZzHYH4teKZyQ3kcyiokp8rXpF2vFy1kUO4Tg+zo7OHgWqYdA6 8SILOHmkAMqdA== From: Nathan Chancellor Date: Wed, 07 Jun 2023 14:20:59 -0700 Subject: [PATCH] percpu: Fix self-assignment of __old in raw_cpu_generic_try_cmpxchg() MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20230607-fix-shadowing-in-raw_cpu_generic_try_cmpxchg-v1-1-8f0a3d930d43@kernel.org> X-B4-Tracking: v=1; b=H4sIALr0gGQC/5XOQQ6CMBCF4auQrp1YqErwKsQ07TC0E2NpWhUM4 e4Wb+DyX7wvbxWZElMW12oVid6ceQol6kMl0JvgCHgoLRrZKHmRLYy8QPZmmGYODjhAMrPG+NK OQqFQP9NH4yMu6B2c287Wsh6VVJ0opDWZwCYT0O+oPR3/4qzB+87ERGX3e93ftu0LMaPdpcUAA AA= To: peterz@infradead.org Cc: mark.rutland@arm.com, arnd@arndb.de, ndesaulniers@google.com, trix@redhat.com, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, patches@lists.linux.dev, Nathan Chancellor X-Mailer: b4 0.13-dev X-Developer-Signature: v=1; a=openpgp-sha256; l=2305; i=nathan@kernel.org; h=from:subject:message-id; bh=jSlEKrCnMK95pETVHXEKH30RppvMmXwHnRIAJknEjUM=; b=owGbwMvMwCEmm602sfCA1DTG02pJDCkNX85eNOfhDjcKuLy2JurVr61OW50+rKrcYHno8Ilzn AILwmrVO0pZGMQ4GGTFFFmqH6seNzScc5bxxqlJMHNYmUCGMHBxCsBEarQY/hdoJqv95NH523yh MTbcNuy6y4dr93aXT/n52WqjdPPVk62MDCfvfrb5LPFxxnGzrafiry/wYdZbxXv/CZv6lzfPN5j /28wOAA== X-Developer-Key: i=nathan@kernel.org; a=openpgp; fpr=2437CB76E544CB6AB3D9DFD399739260CB6CB716 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org After commit c5c0ba953b8c ("percpu: Add {raw,this}_cpu_try_cmpxchg()"), clang built ARCH=3Darm and ARCH=3Darm64 kernels with CONFIG_INIT_STACK_NONE started panicking on boot in alloc_vmap_area(): [ 0.000000] kernel BUG at mm/vmalloc.c:1638! [ 0.000000] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT = SMP [ 0.000000] Modules linked in: [ 0.000000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.4.0-rc2-ARCH+ = #1 [ 0.000000] Hardware name: linux,dummy-virt (DT) [ 0.000000] pstate: 200000c9 (nzCv daIF -PAN -UAO -TCO -DIT -SSBS BTYP= E=3D--) [ 0.000000] pc : alloc_vmap_area+0x7ec/0x7f8 [ 0.000000] lr : alloc_vmap_area+0x7e8/0x7f8 Compiling mm/vmalloc.c with W=3D2 reveals an instance of -Wshadow, which helps uncover that through macro expansion, '__old =3D *(ovalp)' in raw_cpu_generic_try_cmpxchg() can become '__old =3D *(&__old)' through raw_cpu_generic_cmpxchg(), which results in garbage being assigned to the inner __old and the cmpxchg not working properly. Add an extra underscore to __old in raw_cpu_generic_try_cmpxchg() so that there is no more self-assignment, which resolves the panics. Closes: https://github.com/ClangBuiltLinux/linux/issues/1868 Debugged-by: Nick Desaulniers Fixes: c5c0ba953b8c ("percpu: Add {raw,this}_cpu_try_cmpxchg()") Signed-off-by: Nathan Chancellor --- include/asm-generic/percpu.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h index 68c410e85cd7..94cbd50cc870 100644 --- a/include/asm-generic/percpu.h +++ b/include/asm-generic/percpu.h @@ -101,9 +101,9 @@ do { \ #define raw_cpu_generic_try_cmpxchg(pcp, ovalp, nval) \ ({ \ typeof(pcp) *__p =3D raw_cpu_ptr(&(pcp)); \ - typeof(pcp) __val =3D *__p, __old =3D *(ovalp); \ + typeof(pcp) __val =3D *__p, ___old =3D *(ovalp); \ bool __ret; \ - if (__val =3D=3D __old) { \ + if (__val =3D=3D ___old) { \ *__p =3D nval; \ __ret =3D true; \ } else { \ --- base-commit: ef558b4b7bbbf7e115c87e4da21ce86444d6ec3b change-id: 20230607-fix-shadowing-in-raw_cpu_generic_try_cmpxchg-579b101f30= 39 Best regards, --=20 Nathan Chancellor