在 2021/7/15 7:29, Andrew Morton 写道:
On Wed, 14 Jul 2021 09:59:59 +0800 Chen Wandun <chenwandun@xxxxxxxxxx> wrote:
commit f608788cd2d6 ("mm/vmalloc: use rb_tree instead of list for vread()
lookups") use rb_tree instread of list to speed up lookup, but function
__find_vmap_area is try to find a vmap_area that include target address,
if target address is smaller than the leftmost node in vmap_area_root,
it will return NULL, then vread will read nothing. This behavior is
different from the primitive semantics.
What is "the primitive semantics"? Does this refer to behaviour prior
to f608788cd2d6?
If address is smaller than the leftmost node in vmap_area_root and
the read size is big enough when reading [addr, addr + count),
"the primitive semantics" will fill holes by zero and copy valid vmap_area.
In such scenario, f608788cd2d6 will read noting.
The correct way is find the first vmap_are that bigger than target addr,
that is what function find_vmap_area_exceed_addr does.
Is this problem observable from userspace? If so, what are the effects
and what must an application do to trigger it?
Reading /proc/kcore will be affected.
Thanks,
Wandun
.
