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Date:   Fri, 30 Nov 2018 11:56:07 -0800
From:   Omar Sandoval <osandov@osandov.com>
To:     Huijin Park <huijin.park@samsung.com>
Cc:     Andreas Dilger <adilger.kernel@dilger.ca>,
        Michael Callahan <michaelcallahan@fb.com>,
        Omar Sandoval <osandov@fb.com>, js07.lee@samsung.com,
        Huijin Park <bbanghj.park@gmail.com>,
        linux-block@vger.kernel.org, linux-ext4@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH,1/2] genhd: avoid overflow of sectors in disk_stats
Message-ID: <20181130195607.GA27411@vader>
References: <CGME20181130093318eucas1p24feb8e649c8f244ce149a7f87e43c828@eucas1p2.samsung.com>
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On Fri, Nov 30, 2018 at 04:32:40AM -0500, Huijin Park wrote:
> From: "huijin.park" <huijin.park@samsung.com>
> 
> This patch changes the 'sectors' type to an u64.
> In 32 bit system, the 'sectors' can accumulate up to about 2TiB.
> If a 32 bit system makes i/o over 2TiB while running,
> the 'sectors' will overflow.
> As a result, the part_stat_read(sectors), the diskstats in proc and
> the (lifetime|session)_write_kbytes in sysfs return invalid statistic.

What about parsers which expect it to be an unsigned long? E.g., iostat:
https://github.com/sysstat/sysstat/blob/v12.1.1/rd_stats.c#L736

At least with glibc, scanf seems to truncate sanely, but this appears to
be undefined.

> Signed-off-by: huijin.park <huijin.park@samsung.com>
> ---
>  block/genhd.c         |    6 +++---
>  include/linux/genhd.h |    2 +-
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/block/genhd.c b/block/genhd.c
> index 0145bcb..7518dcd 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -1343,10 +1343,10 @@ static int diskstats_show(struct seq_file *seqf, void *v)
>  		part_stat_unlock();
>  		part_in_flight(gp->queue, hd, inflight);
>  		seq_printf(seqf, "%4d %7d %s "
> -			   "%lu %lu %lu %u "
> -			   "%lu %lu %lu %u "
> +			   "%lu %lu %llu %u "
> +			   "%lu %lu %llu %u "
>  			   "%u %u %u "
> -			   "%lu %lu %lu %u\n",
> +			   "%lu %lu %llu %u\n",
>  			   MAJOR(part_devt(hd)), MINOR(part_devt(hd)),
>  			   disk_name(gp, hd->partno, buf),
>  			   part_stat_read(hd, ios[STAT_READ]),
> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
> index 0c5ee17..5bf86f9 100644
> --- a/include/linux/genhd.h
> +++ b/include/linux/genhd.h
> @@ -84,7 +84,7 @@ struct partition {
>  
>  struct disk_stats {
>  	u64 nsecs[NR_STAT_GROUPS];
> -	unsigned long sectors[NR_STAT_GROUPS];
> +	u64 sectors[NR_STAT_GROUPS];
>  	unsigned long ios[NR_STAT_GROUPS];
>  	unsigned long merges[NR_STAT_GROUPS];
>  	unsigned long io_ticks;
> -- 
> 1.7.9.5
>