Messages in this thread | | | Subject | Re: [PATCH] mm/vmalloc: fix wrong behavior in vread | From | Chen Wandun <> | Date | Thu, 15 Jul 2021 10:03:37 +0800 |
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在 2021/7/15 7:29, Andrew Morton 写道: > On Wed, 14 Jul 2021 09:59:59 +0800 Chen Wandun <chenwandun@huawei.com> 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
> .
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