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From:   Souptick Joarder <jrdr.linux@gmail.com>
Date:   Wed, 25 Nov 2020 21:19:34 +0530
Message-ID: <CAFqt6zY5uoU8E9fhHQ2wU7V5C5b9WtNXXMGCEbmaEYQ3pWgvPQ@mail.gmail.com>
Subject: Re: [PATCH] mm: cma: improve pr_debug log in cma_release()
To:     Charan Teja Reddy <charante@codeaurora.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Linux-MM <linux-mm@kvack.org>, linux-kernel@vger.kernel.org,
        vinmenon@codeaurora.org
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On Wed, Nov 25, 2020 at 9:02 PM Charan Teja Reddy
<charante@codeaurora.org> 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@codeaurora.org>

Reviewed-by: Souptick Joarder <jrdr.linux@gmail.com>

> ---
>  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);
>
> --
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
> member of the Code Aurora Forum, hosted by The Linux Foundation
>
>