| Date | Wed, 11 Dec 2013 18:08:44 +0100 | From | Oleg Nesterov <> | Subject | Re: process 'stuck' at exit. |
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On 12/10, Linus Torvalds wrote: > > I think what happens is: > - get_user_pages_fast(address, 1, 1, &page) fails (because it's read-only) > - get_user_pages_fast(address, 1, 0, &page) succeeds and gets a large-page > - __get_user_pages_fast(address, 1, 1, &page) fails (because it's read-only). > > so what triggers this is likely that Dave now does large-pages, and > one of them is a read-only mapping. > > So I would suggest replacing the second "1" in the > __get_user_pages_fast() call with a "!ro" instead. So how about this > second patch instead (the access_ok() move remains).
I know almost nothing about THP, but why we may need write == true in this case?
IOW,
> - if (likely(__get_user_pages_fast(address, 1, 1, &page) == 1)) { > + if (likely(__get_user_pages_fast(address, 1, !ro, &page) == 1)) {
can't if (likely(__get_user_pages_fast(address, 1, 0, &page) == 1)) {
work?
I have to admit, I do not understand why we can't avoid this altogether.
__get_page_tail() can find the stable ->first_page, why get_futex_key() can't ?
Oleg.
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