linux-kernel - Re: [PATCH] LIB: remove unmatched write_lock() in gen_pool

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Date:	Mon, 15 Jun 2009 15:54:24 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Steve Wise <swise@...ngridcomputing.com>
Cc:	trivial@...nel.org, zygo.blaxell@...dros.com,
	linux-kernel@...r.kernel.org, Jes Sorensen <jes@...ined-monkey.org>
Subject: Re: [PATCH] LIB: remove unmatched write_lock() in gen_pool_destroy

On Mon, 15 Jun 2009 17:30:32 -0500
Steve Wise <swise@...ngridcomputing.com> wrote:

> Andrew Morton wrote:
> > On Mon, 15 Jun 2009 23:35:31 +0200 (CEST)
> > Jiri Kosina <trivial@...nel.org> wrote:
> >
> >   
> >>> -	write_lock(&pool->lock);
> >>>  	list_for_each_safe(_chunk, _next_chunk, &pool->chunks) {
> >>>  		chunk = list_entry(_chunk, struct gen_pool_chunk, next_chunk);
> >>>  		list_del(&chunk->next_chunk);
> >>> -- 
> >>> 1.5.6.5
> >>>
> >>>       
> >> Hi Zygo,
> >>
> >> this doesn't really qualify for trivial tree, as it introduces a 
> >> significant code change. Adding some CCs.
> >>     
> >
> > yep, I merged it, thanks.
> >
> > I wonder why drivers/infiniband/hw/cxgb3 users never noticed this.
> >   
> 
> I seem to remember trying to get this removed a few years ago and the 
> owner didn't want it removed...
> 

void gen_pool_destroy(struct gen_pool *pool)
{
	struct list_head *_chunk, *_next_chunk;
	struct gen_pool_chunk *chunk;
	int order = pool->min_alloc_order;
	int bit, end_bit;


	write_lock(&pool->lock);
	list_for_each_safe(_chunk, _next_chunk, &pool->chunks) {
		chunk = list_entry(_chunk, struct gen_pool_chunk, next_chunk);
		list_del(&chunk->next_chunk);

		end_bit = (chunk->end_addr - chunk->start_addr) >> order;
		bit = find_next_bit(chunk->bits, end_bit, 0);
		BUG_ON(bit < end_bit);

		kfree(chunk);
	}
	kfree(pool);
	return;
}

The write_lock is unneeded and wrong.  Because if any other thread of
control is concurrently playing with this pool, it will sometimes do a
use-after-free.

So no other thread of control should have access to this pool, so
there's no need for the write_lock().
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