[PATCH v4 4/4] mm/vmalloc: don't assume vmap_area w/o VM_VM_AREA flag is vm_map_ram allocation

[Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>]

There is a race window between vmap_area free and show vmap_area information.

	A                                                B

remove_vm_area
spin_lock(&vmap_area_lock);
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 is introduced by commit: d4033afd(mm, vmalloc: iterate vmap_area_list, 
instead of vmlist, in vmallocinfo()). This patch fix it by drop the assumption and 
keep not dump vm_map_ram allocation information as the logic before that commit.

Signed-off-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
---
 mm/vmalloc.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 5368b17..62b7932 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2586,13 +2586,6 @@ static int s_show(struct seq_file *m, void *p)
 	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);
-		return 0;
-	}
-
 	v = va->vm;
 
 	seq_printf(m, "0x%pK-0x%pK %7ld",
-- 
1.8.1.2

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