linux-kernel - Re: [PATCH 6/8] padata: Use a timer to handle the reorder queues

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Message-Id: <20100429160644.4dee414d.akpm@linux-foundation.org>
Date:	Thu, 29 Apr 2010 16:06:44 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Steffen Klassert <steffen.klassert@...unet.com>
Cc:	Herbert Xu <herbert@...dor.hengli.com.au>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/8] padata: Use a timer to handle the reorder queues

On Thu, 29 Apr 2010 14:43:37 +0200
Steffen Klassert <steffen.klassert@...unet.com> wrote:

> padata_get_next had a bogus check that returned always true,
> so the try_again loop in padata_reorder was never taken.

A better changelog would have told us what this "bogus check" _is_.

> This can lead to object leaks in some rare cases.

And a better changelog would describe those leaks!

> This patch
> implements a timer that processes the reorder queues if noone
> else does it in appropriate time.

Under what circumstances would "noone else do it in appropriate time"? 
Would that be a bug, or what?

> @@ -273,13 +274,22 @@ try_again:
>  
>  	spin_unlock_bh(&pd->lock);
>  
> -	if (atomic_read(&pd->reorder_objects))
> -		goto try_again;
> +	if (atomic_read(&pd->reorder_objects)
> +			&& !(pinst->flags & PADATA_RESET))
> +		mod_timer(&pd->timer, jiffies + HZ);
> +	else
> +		del_timer(&pd->timer);
>  
> -out:
>  	return;
>  }

I'd feel more comfortable if the above was in the locked region.  Is
there a race whereby another CPU can set pd->reorder_objects, but we
forgot to arm the timer?


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