Changelog:
*v4 -> v5: return directly for !VM_VM_AREA case and remove (VM_LAZY_FREE | VM_LAZY_FREEING) check
There is a race window between vmap_area tear down and show vmap_area information.
A B
remove_vm_area
spin_lock(&vmap_area_lock);
va->vm = NULL;
va->flags &= ~VM_VM_AREA;
spin_unlock(&vmap_area_lock);
spin_lock(&vmap_area_lock);
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;
}
free_unmap_vmap_area(va);
flush_cache_vunmap
free_unmap_vmap_area_noflush
unmap_vmap_area
free_vmap_area_noflush
va->flags |= VM_LAZY_FREE
The assumption !VM_VM_AREA represents vm_map_ram allocation is introduced by
commit: 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: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
---
mm/vmalloc.c | 15 ++++++---------
1 file changed, 6 insertions(+), 9 deletions(-)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 5368b17..9b75028 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2582,16 +2582,13 @@ 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;
--
1.8.1.2
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