linux-kernel - Re: [PATCH] libfc: fix seconds_since_last

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Message-ID: <20161115091840.7cldqui4dpi7nrz5@linux-x5ow.site>
Date:   Tue, 15 Nov 2016 10:18:40 +0100
From:   Johannes Thumshirn <jthumshirn@...e.de>
To:     Bart Van Assche <Bart.VanAssche@...disk.com>
Cc:     "Martin K . Petersen" <martin.petersen@...cle.com>,
        James Bottomley <jejb@...ux.vnet.ibm.com>,
        Hannes Reinecke <hare@...e.de>,
        Christoph Hellwig <hch@...radead.org>,
        Linux SCSI Mailinglist <linux-scsi@...r.kernel.org>,
        Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] libfc: fix seconds_since_last_reset miscalculation

On Tue, Nov 08, 2016 at 03:04:43PM +0000, Bart Van Assche wrote:

[...]

> Hello Johannes,
> 
> I think the above code will miscalculate seconds_since_last_reset if 
> 'jiffies' wraps around after an lport has been created and before 
> seconds_since_last_reset is computed. Shouldn't seconds_since_last_reset 
> be computed as follows?
> 
> 	fc_stats->seconds_since_last_reset = (jiffies - boot_time) / HZ;

But what happens when jiffies - boot_time becomes negative? Then we
reintroduce the bug again and have 'fcoeadm -s' show weird values.

Byte,
	Johannes
-- 
Johannes Thumshirn                                          Storage
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