linux-kernel - Re: [PATCH 1/2] mempool: drop unnecessary and incorrect BUG_ON() from mempool

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Message-Id: <20111221162519.b7fc3a79.akpm@linux-foundation.org>
Date:	Wed, 21 Dec 2011 16:25:19 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mempool: drop unnecessary and incorrect BUG_ON()
 from mempool_destroy()

On Wed, 21 Dec 2011 16:18:00 -0800
Tejun Heo <tj@...nel.org> wrote:

> mempool_destroy() is a thin wrapper around free_pool().  The only
> thing it adds is BUG_ON(pool->curr_nr != pool->min_nr).  The intention
> seems to be to enforce that all allocated elements are freed; however,
> the BUG_ON() can't achieve that (it doesn't know anything about
> objects above min_nr) and incorrect as mempool_resize() is allowed to
> leave the pool extended but not filled.  Furthermore, panicking is way
> worse than any memory leak and there are better debug tools to track
> memory leaks.
> 
> Drop the BUG_ON() from mempool_destory() and as that leaves the
> function identical to free_pool(), replace it.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: stable@...nel.org

(that's stable@...r.kernel.org)

> ---
> These patches are on top of "mempool: fix and document synchronization
> and memory barrier usage" patch[1].  Both are fixes and it probably is
> a good idea to forward to -stable.

I'm not sure that either of these are suitable for -stable.  There's no
demonstrated problem, nor even a likely theoretical one, is there?

If we do decide to backport, I don't think the -stable guys will want
the large-but-nice comment-adding patch so both these patches would need to
be reworked for -stable usage.  The first patch does apply successfully
to mainline.  The second does not.

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