linux-kernel - Re: [PATCH 1/1] Add check for dirty_writeback_interval in bdi_wakeup_thread

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Date:	Mon, 18 Apr 2011 10:02:04 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Raghavendra D Prabhu <rprabhu@...hang.net>
Cc:	linux-mm@...ck.org, Artem Bityutskiy <Artem.Bityutskiy@...ia.com>,
	Jens Axboe <jaxboe@...ionio.com>,
	Christoph Hellwig <hch@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] Add check for dirty_writeback_interval in
 bdi_wakeup_thread_delayed

On Sun, Apr 17, 2011 at 09:53:08PM +0530, Raghavendra D Prabhu wrote:
> In the function bdi_wakeup_thread_delayed, no checks are performed on
> dirty_writeback_interval unlike other places and timeout is being set to
> zero as result, thus defeating the purpose. So, I have changed it to be
> passed default value of interval which is 500 centiseconds, when it is
> set to zero.
> I have also verified this and tested it.
> 
> Signed-off-by: Raghavendra D Prabhu <rprabhu@...hang.net>
> ---
>  mm/backing-dev.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index befc875..d06533c 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -336,7 +336,10 @@ void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
>  {
>  	unsigned long timeout;
> -	timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
> +	if (dirty_writeback_interval)
> +		timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
> +	else
> +		timeout = msecs_to_jiffies(5000);
>  	mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout);
>  }

Isn't the problem that the sysctl handler does not have a min/max
valid value set? I.e. to prevent invalid values from being set in
the first place?

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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