From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751279AbdILDpa (ORCPT ); Mon, 11 Sep 2017 23:45:30 -0400 Received: from mail-pg0-f67.google.com ([74.125.83.67]:33790 "EHLO mail-pg0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751041AbdILDp2 (ORCPT ); Mon, 11 Sep 2017 23:45:28 -0400 X-Google-Smtp-Source: ADKCNb5i95nSuQ+Gan4ieYBP6DiUlJsZXu3ZacANVEQXHc2sOTGidvE0BR213J7d15By6YYuYwjUnw== From: Guenter Roeck To: Ley Foon Tan Cc: nios2-dev@lists.rocketboards.org, linux-kernel@vger.kernel.org, Guenter Roeck , Laura Abbott , Kees Cook , Daniel Micay Subject: [PATCH] nios2: time: Read timer in get_cycles only if initialized Date: Mon, 11 Sep 2017 20:45:26 -0700 Message-Id: <1505187926-19399-1-git-send-email-linux@roeck-us.net> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Mainline crashes as follows when running nios2 images. On node 0 totalpages: 65536 free_area_init_node: node 0, pgdat c8408fa0, node_mem_map c8726000 Normal zone: 512 pages used for memmap Normal zone: 0 pages reserved Normal zone: 65536 pages, LIFO batch:15 Unable to handle kernel NULL pointer dereference at virtual address 00000000 ea = c8003cb0, ra = c81cbf40, cause = 15 Kernel panic - not syncing: Oops Problem is seen because get_cycles() is called before the timer it depends on is initialized. Returning 0 in that situation fixes the problem. Fixes: 33d72f3822d7 ("init/main.c: extract early boot entropy from the ..") Cc: Laura Abbott Cc: Kees Cook Cc: Daniel Micay Signed-off-by: Guenter Roeck --- Taking a stab at the problem. Fix works for my qemu test. arch/nios2/kernel/time.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/nios2/kernel/time.c b/arch/nios2/kernel/time.c index 645129aaa9a0..20e86209ef2e 100644 --- a/arch/nios2/kernel/time.c +++ b/arch/nios2/kernel/time.c @@ -107,7 +107,10 @@ static struct nios2_clocksource nios2_cs = { cycles_t get_cycles(void) { - return nios2_timer_read(&nios2_cs.cs); + /* Only read timer if it has been initialized */ + if (nios2_cs.timer.base) + return nios2_timer_read(&nios2_cs.cs); + return 0; } EXPORT_SYMBOL(get_cycles); -- 2.7.4