2004-09-21 15:36:22

by Ingo Molnar

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

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 <[email protected]>

--- 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),

2004-09-22 10:57:38

by Jens Axboe

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

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 <[email protected]>
>
> --- 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