linux-kernel - [PATCH 1/1] mm/vmalloc.c: Add an error message if two areas overlap

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Date:   Fri, 10 Jul 2020 21:40:42 +0200
From:   "Uladzislau Rezki (Sony)" <urezki@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Hillf Danton <hdanton@...a.com>,
        Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: [PATCH 1/1] mm/vmalloc.c: Add an error message if two areas overlap

Before triggering a BUG() it would be useful to understand
how two areas overlap between each other. Print information
about start/end addresses of both VAs and their addresses.

For example if both are identical it could mean double free.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
---
 mm/vmalloc.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 5a2b55c8dd9a..1679b01febcd 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -549,8 +549,13 @@ find_va_links(struct vmap_area *va,
 		else if (va->va_end > tmp_va->va_start &&
 				va->va_start >= tmp_va->va_end)
 			link = &(*link)->rb_right;
-		else
+		else {
+			pr_err("Overlaps: 0x%px(0x%lx-0x%lx), 0x%px(0x%lx-0x%lx)\n",
+				va, va->va_start, va->va_end, tmp_va,
+				tmp_va->va_start, tmp_va->va_end);
+
 			BUG();
+		}
 	} while (*link);
 
 	*parent = &tmp_va->rb_node;
@@ -1993,6 +1998,9 @@ static void vmap_init_free_space(void)
 			insert_vmap_area_augment(free, NULL,
 				&free_vmap_area_root,
 					&free_vmap_area_list);
+			insert_vmap_area_augment(free, NULL,
+				&free_vmap_area_root,
+					&free_vmap_area_list);
 		}
 	}
 }
-- 
2.20.1