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

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Date:   Wed, 25 Nov 2020 21:02:21 +0530
From:   Charan Teja Reddy <charante@...eaurora.org>
To:     akpm@...ux-foundation.org, iamjoonsoo.kim@....com,
        linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, vinmenon@...eaurora.org,
        Charan Teja Reddy <charante@...eaurora.org>
Subject: [PATCH] mm: cma: improve pr_debug log in cma_release()

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>
---
 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);

-- 
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