linux-kernel - Re: [PATCH] mm: cma: improve pr_debug log in cma

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Message-ID: <f6744947-72b5-39e0-9eb0-7f3f09f773b3@suse.cz>
Date:   Fri, 27 Nov 2020 16:49:43 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Charan Teja Reddy <charante@...eaurora.org>,
        akpm@...ux-foundation.org, iamjoonsoo.kim@....com,
        linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, vinmenon@...eaurora.org
Subject: Re: [PATCH] mm: cma: improve pr_debug log in cma_release()

On 11/25/20 4:32 PM, Charan Teja Reddy wrote:
> It is required to print 'count' of pages, along with the pages, passed
> to cma_release to debug the cases of mismatched count value passed
> between cma_alloc() and cma_release() from a code path.
> 
> As an example, consider the below scenario:
> 1) CMA pool size is 4MB and
> 2) User doing the erroneous step of allocating 2 pages but freeing 1
> page in a loop from this CMA pool.
> The step 2 causes cma_alloc() to return NULL at one point of time
> because of -ENOMEM condition.
> 
> And the current pr_debug logs is not giving the info about these types
> of allocation patterns because of count value not being printed in
> cma_release().
> 
> We are printing the count value in the trace logs, just extend the same
> to pr_debug logs too.
> 
> Signed-off-by: Charan Teja Reddy <charante@...eaurora.org>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>   mm/cma.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/cma.c b/mm/cma.c
> index 7f415d7..07c904b 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -512,7 +512,7 @@ bool cma_release(struct cma *cma, const struct page *pages, unsigned int count)
>   	if (!cma || !pages)
>   		return false;
>   
> -	pr_debug("%s(page %p)\n", __func__, (void *)pages);
> +	pr_debug("%s(page %p, count %zu)\n", __func__, (void *)pages, count);
>   
>   	pfn = page_to_pfn(pages);
>   
>