Commit c2ce8c14 authored by Wanpeng Li's avatar Wanpeng Li Committed by Linus Torvalds

mm/vmalloc: fix show vmap_area information race with vmap_area tear down

There is a race window between vmap_area tear down and show vmap_area

	A                                                B

va->vm = NULL;
va->flags &= ~VM_VM_AREA;
						if (va->flags & (VM_LAZY_FREE | VM_LAZY_FREEZING))
							return 0;
						if (!(va->flags & VM_VM_AREA)) {
							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);
							return 0;
			va->flags |= VM_LAZY_FREE

The assumption !VM_VM_AREA represents vm_map_ram allocation is
introduced by d4033afd ("mm, vmalloc: iterate vmap_area_list,
instead of vmlist, in vmallocinfo()").

However, !VM_VM_AREA also represents vmap_area is being tear down in
race window mentioned above.  This patch fix it by don't dump any
information for !VM_VM_AREA case and also remove (VM_LAZY_FREE |
VM_LAZY_FREEING) check since they are not possible for !VM_VM_AREA case.
Suggested-by: default avatarJoonsoo Kim <>
Acked-by: default avatarKOSAKI Motohiro <>
Signed-off-by: default avatarWanpeng Li <>
Cc: Mitsuo Hayasaka <>
Cc: Zhang Yanfei <>
Cc: David Rientjes <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 3722e13c
......@@ -2578,15 +2578,12 @@ static int s_show(struct seq_file *m, void *p)
struct vmap_area *va = p;
struct vm_struct *v;
if (va->flags & (VM_LAZY_FREE | VM_LAZY_FREEING))
return 0;
if (!(va->flags & VM_VM_AREA)) {
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);
* s_show can encounter race with remove_vm_area, !VM_VM_AREA on
* behalf of vmap area is being tear down or vm_map_ram allocation.
if (!(va->flags & VM_VM_AREA))
return 0;
v = va->vm;
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