On Sun, May 03, 2020 at 09:43:41AM +0100, Nikolaus Rath wrote:
> Here's what I got:
>
> [ 221.277260] page:ffffec4bbd639880 refcount:1 mapcount:0 mapping:0000000000000000 index:0xd9
> [ 221.277265] flags: 0x17ffffc0000097(locked|waiters|referenced|uptodate|lru)
> [ 221.277269] raw: 0017ffffc0000097 ffffec4bbd62f048 ffffec4bbd619308 0000000000000000
> [ 221.277271] raw: 00000000000000d9 0000000000000000 00000001ffffffff ffff9aec11beb000
> [ 221.277272] page dumped because: fuse: trying to steal weird page
> [ 221.277273] page->mem_cgroup:ffff9aec11beb000
Great! Here's the condition:
if (page_mapcount(page) ||
page->mapping != NULL ||
page_count(page) != 1 ||
(page->flags & PAGE_FLAGS_CHECK_AT_PREP &
~(1 << PG_locked |
1 << PG_referenced |
1 << PG_uptodate |
1 << PG_lru |
1 << PG_active |
1 << PG_reclaim))) {
mapcount is 0, mapping is NULL, refcount is 1, so that's all fine.
flags has 'waiters' set, which is not in the allowed list. I don't
know the internals of FUSE, so I don't know why that is.
Also, page_count() is unstable. Unless there has been an RCU grace period
between when the page was freed and now, a speculative reference may exist
from the page cache. So I would say this is a bad thing to check for.
Thanks for the swift provision of the debugging data!
