linux-kernel - [PATCH 5.1 020/155] mm/cma.c: fix the bitmap status to show failed allocation reason

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Date:   Thu, 13 Jun 2019 10:32:12 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Yue Hu <huyue2@...ong.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Ingo Molnar <mingo@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Laura Abbott <labbott@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.1 020/155] mm/cma.c: fix the bitmap status to show failed allocation reason

[ Upstream commit 2b59e01a3aa665f751d1410b99fae9336bd424e1 ]

Currently one bit in cma bitmap represents number of pages rather than
one page, cma->count means cma size in pages. So to find available pages
via find_next_zero_bit()/find_next_bit() we should use cma size not in
pages but in bits although current free pages number is correct due to
zero value of order_per_bit. Once order_per_bit is changed the bitmap
status will be incorrect.

The size input in cma_debug_show_areas() is not correct.  It will
affect the available pages at some position to debug the failure issue.

This is an example with order_per_bit = 1

Before this change:
[    4.120060] cma: number of available pages: 1@...4@...+7@...+7@...+7@...+7@...+7@...+7@...+3@...+3@...+3@...+3@...+3@...+3@...+3@...+3@...+3@...+3@...+3@...+3@...+3@...+3@...+3@...+19@...+15@...+512@...=> 638 free of 1024 total pages

After this change:
[    4.143234] cma: number of available pages: 2@...8@...+14@...+14@...+14@...+14@...+14@...+14@...+6@...+6@...+6@...+6@...+6@...+6@...+6@...+6@...+6@...+6@...+6@...+6@...+6@...+6@...+6@...+38@...+30@...=> 252 free of 1024 total pages

Obviously the bitmap status before is incorrect.

Link: http://lkml.kernel.org/r/20190320060829.9144-1-zbestahu@gmail.com
Signed-off-by: Yue Hu <huyue2@...ong.com>
Reviewed-by: Andrew Morton <akpm@...ux-foundation.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Mike Rapoport <rppt@...ux.vnet.ibm.com>
Cc: Randy Dunlap <rdunlap@...radead.org>
Cc: Laura Abbott <labbott@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 mm/cma.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/mm/cma.c b/mm/cma.c
index 8cb95cd1193a..5e36d7418031 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -369,23 +369,26 @@ err:
 #ifdef CONFIG_CMA_DEBUG
 static void cma_debug_show_areas(struct cma *cma)
 {
-	unsigned long next_zero_bit, next_set_bit;
+	unsigned long next_zero_bit, next_set_bit, nr_zero;
 	unsigned long start = 0;
-	unsigned int nr_zero, nr_total = 0;
+	unsigned long nr_part, nr_total = 0;
+	unsigned long nbits = cma_bitmap_maxno(cma);
 
 	mutex_lock(&cma->lock);
 	pr_info("number of available pages: ");
 	for (;;) {
-		next_zero_bit = find_next_zero_bit(cma->bitmap, cma->count, start);
-		if (next_zero_bit >= cma->count)
+		next_zero_bit = find_next_zero_bit(cma->bitmap, nbits, start);
+		if (next_zero_bit >= nbits)
 			break;
-		next_set_bit = find_next_bit(cma->bitmap, cma->count, next_zero_bit);
+		next_set_bit = find_next_bit(cma->bitmap, nbits, next_zero_bit);
 		nr_zero = next_set_bit - next_zero_bit;
-		pr_cont("%s%u@%lu", nr_total ? "+" : "", nr_zero, next_zero_bit);
-		nr_total += nr_zero;
+		nr_part = nr_zero << cma->order_per_bit;
+		pr_cont("%s%lu@%lu", nr_total ? "+" : "", nr_part,
+			next_zero_bit);
+		nr_total += nr_part;
 		start = next_zero_bit + nr_zero;
 	}
-	pr_cont("=> %u free of %lu total pages\n", nr_total, cma->count);
+	pr_cont("=> %lu free of %lu total pages\n", nr_total, cma->count);
 	mutex_unlock(&cma->lock);
 }
 #else
-- 
2.20.1