Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758019Ab3J2PpX (ORCPT ); Tue, 29 Oct 2013 11:45:23 -0400 Received: from mail-pb0-f45.google.com ([209.85.160.45]:40986 "EHLO mail-pb0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753264Ab3J2PpV (ORCPT ); Tue, 29 Oct 2013 11:45:21 -0400 Date: Tue, 29 Oct 2013 08:45:19 -0700 From: Guenter Roeck To: Boris BREZILLON Cc: Wim Van Sebroeck , Fabio Porcedda , Nicolas Ferre , Guenter Roeck , Yang Wenyou , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-watchdog@vger.kernel.org Subject: Re: [PATCH] watchdog: at91sam9_wdt: various fixes Message-ID: <20131029154519.GB9266@roeck-us.net> References: <20131029075028.GF19704@spo001.leaseweb.com> <1383043053-3520-1-git-send-email-b.brezillon@overkiz.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1383043053-3520-1-git-send-email-b.brezillon@overkiz.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5026 Lines: 153 On Tue, Oct 29, 2013 at 11:37:33AM +0100, Boris BREZILLON wrote: > Fix the secs_to_ticks macro in case 0 is passed as an argument. > > Rework the heartbeat calculation to increase the security margin of the > watchdog reset timer. > > Use the min_heartbeat value instead of the calculated heartbeat value for > the first watchdog reset. > > Signed-off-by: Boris BREZILLON Hi Boris, can you possibly split the three changes into separate patches ? The first is a no-brainer. Gives my opinion of my code review capabilities a slight damper ;-). For the other two problems, it might make sense to describe the problems you are trying to solve. Couple of comments inline. Thanks, Guenter > --- > drivers/watchdog/at91sam9_wdt.c | 35 ++++++++++++++++++++++++----------- > 1 file changed, 24 insertions(+), 11 deletions(-) > > diff --git a/drivers/watchdog/at91sam9_wdt.c b/drivers/watchdog/at91sam9_wdt.c > index 9bd089e..f1b59f1 100644 > --- a/drivers/watchdog/at91sam9_wdt.c > +++ b/drivers/watchdog/at91sam9_wdt.c > @@ -51,7 +51,7 @@ > #define ticks_to_hz_rounddown(t) ((((t) + 1) * HZ) >> 8) > #define ticks_to_hz_roundup(t) (((((t) + 1) * HZ) + 255) >> 8) > #define ticks_to_secs(t) (((t) + 1) >> 8) > -#define secs_to_ticks(s) (((s) << 8) - 1) > +#define secs_to_ticks(s) (s ? (((s) << 8) - 1) : 0) > (s) > #define WDT_MR_RESET 0x3FFF2FFF > > @@ -61,6 +61,11 @@ > /* Watchdog max delta/value in secs */ > #define WDT_COUNTER_MAX_SECS ticks_to_secs(WDT_COUNTER_MAX_TICKS) > > +/* Watchdog heartbeat shift used for security margin: > + * we'll try to rshift the heartbeat value with this value to secure > + * the watchdog reset. */ > +#define WDT_HEARTBEAT_SHIFT 2 > + > /* Hardware timeout in seconds */ > #define WDT_HW_TIMEOUT 2 > > @@ -158,7 +163,9 @@ static int at91_wdt_init(struct platform_device *pdev, struct at91wdt *wdt) > int err; > u32 mask = wdt->mr_mask; > unsigned long min_heartbeat = 1; > + unsigned long max_heartbeat; > struct device *dev = &pdev->dev; > + int shift; > > tmp = wdt_read(wdt, AT91_WDT_MR); > if ((tmp & mask) != (wdt->mr & mask)) { > @@ -181,23 +188,27 @@ static int at91_wdt_init(struct platform_device *pdev, struct at91wdt *wdt) > if (delta < value) > min_heartbeat = ticks_to_hz_roundup(value - delta); > > - wdt->heartbeat = ticks_to_hz_rounddown(value); > - if (!wdt->heartbeat) { > + max_heartbeat = ticks_to_hz_rounddown(value); > + if (!max_heartbeat) { > dev_err(dev, > "heartbeat is too small for the system to handle it correctly\n"); > return -EINVAL; > } > > - if (wdt->heartbeat < min_heartbeat + 4) { > + for (shift = WDT_HEARTBEAT_SHIFT; shift > 0; shift--) { > + if ((max_heartbeat >> shift) < min_heartbeat) > + continue; > + > + wdt->heartbeat = max_heartbeat >> shift; > + break; > + } > + > + if (!shift) > wdt->heartbeat = min_heartbeat; Correct me if I am wrong, but it seems to me that if ((max_heartbeat >> 2) >= min_heartbeat) wdt->heartbeat = max_heartbeat >> 2; else if ((max_heartbeat >> 1) >= min_heartbeat) wdt->heartbeat = max_heartbeat >> 1; else wdt->heartbeat = min_heartbeat; would accomplish the same and be easier to understand. However, given that, I wonder if it is really necessary to bail out above if max_heartbeat is 0. After all, you set heartbeat to min_heartbeat anyway in this case. > + > + if (max_heartbeat < min_heartbeat + 4) > dev_warn(dev, > "min heartbeat and max heartbeat might be too close for the system to handle it correctly\n"); > - if (wdt->heartbeat < 4) > - dev_warn(dev, > - "heartbeat might be too small for the system to handle it correctly\n"); > - } else { > - wdt->heartbeat -= 4; > - } > > if ((tmp & AT91_WDT_WDFIEN) && wdt->irq) { > err = request_irq(wdt->irq, wdt_interrupt, > @@ -213,7 +224,9 @@ static int at91_wdt_init(struct platform_device *pdev, struct at91wdt *wdt) > tmp & wdt->mr_mask, wdt->mr & wdt->mr_mask); > > setup_timer(&wdt->timer, at91_ping, (unsigned long)wdt); > - mod_timer(&wdt->timer, jiffies + wdt->heartbeat); > + /* Use min_heartbeat the first time because the watchdog timer might > + * be running for a long time when we reach this init function. */ /* * Multi-line comment style * * Not really sure I understand what this accomplishes. What problem * are you trying to solve here ? */ > + mod_timer(&wdt->timer, jiffies + min_heartbeat); > > /* Try to set timeout from device tree first */ > if (watchdog_init_timeout(&wdt->wdd, 0, dev)) > -- > 1.7.9.5 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-watchdog" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/