linux-kernel - Re: [PATCH 1/2] dma-debug: add dma_debug_resize_entries() to adjust the number of dma_debug

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Message-ID: <20090414105823.GL3558@elte.hu>
Date:	Tue, 14 Apr 2009 12:58:23 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	linux-kernel@...r.kernel.org, joerg.roedel@....com,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] dma-debug: add dma_debug_resize_entries() to
	adjust the number of dma_debug_entries


* FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> wrote:

> +int dma_debug_resize_entries(u32 num_entries)
> +{
> +	int i, delta, ret = 0;
> +	unsigned long flags;
> +	struct dma_debug_entry *entry;
> +
> +	spin_lock_irqsave(&free_entries_lock, flags);
> +
> +	if (nr_total_entries < num_entries) {
> +		delta = num_entries - nr_total_entries;
> +
> +		for (i = 0; i < delta; i++) {
> +			entry = kzalloc(sizeof(*entry), GFP_ATOMIC);
> +			if (!entry)
> +				break;

hm, using GFP_ATOMIC within a spinlock is not a very nice thing to 
do in general. While this is boot-only and the GFP_ATOMIC will 
likely succeed, this could become non-boot functionality and then 
it's exposed to the momentary VM pressure situation that might make 
GFP_ATOMIC fail.

Please fix this to be GFP_KERNEL.

a small detail:

> +		delta = nr_total_entries - num_entries;
> +
> +		for (i = 0; i < delta && !list_empty(&free_entries); i++) {
> +			entry = __dma_entry_alloc();
> +			kfree(entry);
> +		}
> +
> +		nr_total_entries -= i;
> +	}

Can i != delta ever happen? It would suggest the list length being 
out of sync with the nr_total_entries counter.

	Ingo
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