From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752084AbbEHE2A (ORCPT ); Fri, 8 May 2015 00:28:00 -0400 Received: from mail-ig0-f181.google.com ([209.85.213.181]:36515 "EHLO mail-ig0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750995AbbEHE15 (ORCPT ); Fri, 8 May 2015 00:27:57 -0400 From: Doug Anderson To: wim@iguana.be, linux@roeck-us.net Cc: jszhang@marvell.com, Dmitry Torokhov , Doug Anderson , linux-watchdog@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 1/2] watchdog: dw_wdt: No need for a spinlock Date: Thu, 7 May 2015 21:27:44 -0700 Message-Id: <1431059265-9204-1-git-send-email-dianders@chromium.org> X-Mailer: git-send-email 2.2.0.rc0.207.ga3a616c Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Right now the dw_wdt uses a spinlock to protect dw_wdt_open(). The problem is that while holding the spinlock we call: -> dw_wdt_set_top() -> dw_wdt_top_in_seconds() -> clk_get_rate() -> clk_prepare_lock() -> mutex_lock() Locking a mutex while holding a spinlock is not allowed and leads to warnings like "BUG: spinlock wrong CPU on CPU#1", among other problems. There's no reason to use a spinlock. Only dw_wdt_open() was protected and the test_and_set_bit() at the start of that function protects us anyway. Signed-off-by: Doug Anderson --- Changes in v2: - Don't switch to mutex; just don't use spinlock at all as per Dmitry drivers/watchdog/dw_wdt.c | 7 ------- 1 file changed, 7 deletions(-) diff --git a/drivers/watchdog/dw_wdt.c b/drivers/watchdog/dw_wdt.c index d0bb949..a284abd 100644 --- a/drivers/watchdog/dw_wdt.c +++ b/drivers/watchdog/dw_wdt.c @@ -35,7 +35,6 @@ #include #include #include -#include #include #include #include @@ -61,7 +60,6 @@ MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started " #define WDT_TIMEOUT (HZ / 2) static struct { - spinlock_t lock; void __iomem *regs; struct clk *clk; unsigned long in_use; @@ -177,7 +175,6 @@ static int dw_wdt_open(struct inode *inode, struct file *filp) /* Make sure we don't get unloaded. */ __module_get(THIS_MODULE); - spin_lock(&dw_wdt.lock); if (!dw_wdt_is_enabled()) { /* * The watchdog is not currently enabled. Set the timeout to @@ -190,8 +187,6 @@ static int dw_wdt_open(struct inode *inode, struct file *filp) dw_wdt_set_next_heartbeat(); - spin_unlock(&dw_wdt.lock); - return nonseekable_open(inode, filp); } @@ -348,8 +343,6 @@ static int dw_wdt_drv_probe(struct platform_device *pdev) if (ret) return ret; - spin_lock_init(&dw_wdt.lock); - ret = misc_register(&dw_wdt_miscdev); if (ret) goto out_disable_clk; -- 2.2.0.rc0.207.ga3a616c