linux-kernel - [PATCH v1 4/7] mm/vmalloc: explicitly identify vm_map

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Date:   Sun,  4 Dec 2022 09:30:43 +0800
From:   Baoquan He <bhe@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, stephen.s.brennan@...cle.com, urezki@...il.com,
        willy@...radead.org, akpm@...ux-foundation.org, hch@...radead.org,
        Baoquan He <bhe@...hat.com>
Subject: [PATCH v1 4/7] mm/vmalloc: explicitly identify vm_map_ram area when shown in /proc/vmcoreinfo

Now, by marking VMAP_RAM in vmap_area->flags for vm_map_ram area, we
can clearly differentiate it with other vmalloc areas. So in s_show(),
change the ambiguous checking 'if (!va->vm) to clear
"if (!va->vm && (va->flags & VMAP_RAM))". This let's picks out
vm_map_ram area, and avoids the being unmapped normal vmalloc area to
be mistakenly recognized as vm_map_ram area.

Meanwhile, the code comment above vm_map_ram area checking in s_show()
is not needed any more, remove it here.

Signed-off-by: Baoquan He <bhe@...hat.com>
---
 mm/vmalloc.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index e6b46da3e044..3c60026fb162 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -4181,11 +4181,7 @@ static int s_show(struct seq_file *m, void *p)

 	va = list_entry(p, struct vmap_area, list);

-	/*
-	 * s_show can encounter race with remove_vm_area, !vm on behalf
-	 * of vmap area is being tear down or vm_map_ram allocation.
-	 */
-	if (!va->vm) {
+	if (!va->vm && (va->flags & VMAP_RAM)) {
 		seq_printf(m, "0x%pK-0x%pK %7ld vm_map_ram\n",
 			(void *)va->va_start, (void *)va->va_end,
 			va->va_end - va->va_start);
-- 
2.34.1