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Subject[RFC][PATCH 1/2] vmalloc: reorder unmap and removal entry
> I wonder fs/proc/kcore.c's vmalloc area access needs some fix. let me try.
>
> Thanks,
Finally, I wrote 2 patches. maybe 2/2 is a fix for the bug.
but needs comments.

Comaparing 2 calls, vfree() and vread()
==
vfree()
-> __vumap()
-> remove_vm_area()
-> free_unmap_vmap_area #
-> try_purge_vmap_area_lazy() #
->__purge_vmap_area_lazy(); #
-> unmap_vmap_area() # unmap memory here.
-> write_lock(&vmlist_lock)
remvoe vm_struct from list
write_unlock(&vmlist_lock).
==
vread()
-> read_lock(&vmlist_lock);
get vm_struct -> do memcpy
read_unlock(&vmlist_lock);
==

Hmm, maybe not related to original bug but above order should be fixed.

From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

vmap area should be purged after vm_struct is removed from the list
because vread/vwrite etc...believes the range is valid while it's on
vm_struct list.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
mm/vmalloc.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)

Index: linux-2.6.31-rc4/mm/vmalloc.c
===================================================================
--- linux-2.6.31-rc4.orig/mm/vmalloc.c
+++ linux-2.6.31-rc4/mm/vmalloc.c
@@ -1256,17 +1256,21 @@ struct vm_struct *remove_vm_area(const v
if (va && va->flags & VM_VM_AREA) {
struct vm_struct *vm = va->private;
struct vm_struct *tmp, **p;
-
- vmap_debug_free_range(va->va_start, va->va_end);
- free_unmap_vmap_area(va);
- vm->size -= PAGE_SIZE;
-
+ /*
+ * remove from list and disallow access to this vm_struct
+ * before unmap. (address range confliction is maintained by
+ * vmap.)
+ */
write_lock(&vmlist_lock);
for (p = &vmlist; (tmp = *p) != vm; p = &tmp->next)
;
*p = tmp->next;
write_unlock(&vmlist_lock);

+ vmap_debug_free_range(va->va_start, va->va_end);
+ free_unmap_vmap_area(va);
+ vm->size -= PAGE_SIZE;
+
return vm;
}
return NULL;


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