From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:46078 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754282AbdJJT7s (ORCPT ); Tue, 10 Oct 2017 15:59:48 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Mark Rutland , Arnd Bergmann , Christoph Lameter , Peter Zijlstra , Pranith Kumar , Tejun Heo , Thomas Gleixner , linux-arch@vger.kernel.org Subject: [PATCH 4.9 080/105] percpu: make this_cpu_generic_read() atomic w.r.t. interrupts Date: Tue, 10 Oct 2017 21:50:51 +0200 Message-Id: <20171010192546.077105489@linuxfoundation.org> In-Reply-To: <20171010192533.717049376@linuxfoundation.org> References: <20171010192533.717049376@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Mark Rutland commit e88d62cd4b2f0b1ae55e9008e79c2794b1fc914d upstream. As raw_cpu_generic_read() is a plain read from a raw_cpu_ptr() address, it's possible (albeit unlikely) that the compiler will split the access across multiple instructions. In this_cpu_generic_read() we disable preemption but not interrupts before calling raw_cpu_generic_read(). Thus, an interrupt could be taken in the middle of the split load instructions. If a this_cpu_write() or RMW this_cpu_*() op is made to the same variable in the interrupt handling path, this_cpu_read() will return a torn value. For native word types, we can avoid tearing using READ_ONCE(), but this won't work in all cases (e.g. 64-bit types on most 32-bit platforms). This patch reworks this_cpu_generic_read() to use READ_ONCE() where possible, otherwise falling back to disabling interrupts. Signed-off-by: Mark Rutland Cc: Arnd Bergmann Cc: Christoph Lameter Cc: Peter Zijlstra Cc: Pranith Kumar Cc: Tejun Heo Cc: Thomas Gleixner Cc: linux-arch@vger.kernel.org Signed-off-by: Tejun Heo Signed-off-by: Greg Kroah-Hartman --- include/asm-generic/percpu.h | 24 ++++++++++++++++++++++-- 1 file changed, 22 insertions(+), 2 deletions(-) --- a/include/asm-generic/percpu.h +++ b/include/asm-generic/percpu.h @@ -115,15 +115,35 @@ do { \ (__ret); \ }) -#define this_cpu_generic_read(pcp) \ +#define __this_cpu_generic_read_nopreempt(pcp) \ ({ \ typeof(pcp) __ret; \ preempt_disable_notrace(); \ - __ret = raw_cpu_generic_read(pcp); \ + __ret = READ_ONCE(*raw_cpu_ptr(&(pcp))); \ preempt_enable_notrace(); \ __ret; \ }) +#define __this_cpu_generic_read_noirq(pcp) \ +({ \ + typeof(pcp) __ret; \ + unsigned long __flags; \ + raw_local_irq_save(__flags); \ + __ret = raw_cpu_generic_read(pcp); \ + raw_local_irq_restore(__flags); \ + __ret; \ +}) + +#define this_cpu_generic_read(pcp) \ +({ \ + typeof(pcp) __ret; \ + if (__native_word(pcp)) \ + __ret = __this_cpu_generic_read_nopreempt(pcp); \ + else \ + __ret = __this_cpu_generic_read_noirq(pcp); \ + __ret; \ +}) + #define this_cpu_generic_to_op(pcp, val, op) \ do { \ unsigned long __flags; \