Re: [patch] fix diskstats_show() accounting with PREEMPT

[Jens Axboe]

On Tue, Sep 21 2004, Ingo Molnar wrote:
> 
> there is another (minor) bug that the smp_processor_id() debugger
> unearthed: diskstats_show() could do a disk_round_stats() ->
> disk_stat_add() with preemption enabled - possibly resulting in losing
> statistics updates.
> 
> Patch attached. (The overwhelming majority of disk_stat_add() callers
> have preemption disabled so fixing the remaining two was the best.)
> 
> 	Ingo
> 
> Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
> 
> --- linux/drivers/block/genhd.c.orig	
> +++ linux/drivers/block/genhd.c	
> @@ -365,7 +365,9 @@ static ssize_t disk_size_read(struct gen
>  
>  static ssize_t disk_stats_read(struct gendisk * disk, char *page)
>  {
> +	preempt_disable();
>  	disk_round_stats(disk);
> +	preempt_enable();
>  	return sprintf(page,
>  		"%8u %8u %8llu %8u "
>  		"%8u %8u %8llu %8u "
> @@ -494,7 +496,9 @@ static int diskstats_show(struct seq_fil
>  				"\n\n");
>  	*/
>   
> +	preempt_disable();
>  	disk_round_stats(gp);
> +	preempt_enable();
>  	seq_printf(s, "%4d %4d %s %u %u %llu %u %u %u %llu %u %u %u %u\n",
>  		gp->major, n + gp->first_minor, disk_name(gp, n, buf),
>  		disk_stat_read(gp, reads), disk_stat_read(gp, read_merges),

Looks fine, thanks Ingo.

-- 
Jens Axboe

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