On Sun, 2013-06-16 at 12:00 +1000, Benjamin Herrenschmidt wrote: > So at this point, hash_page might *still* see the old pmd. Unless I > missed something, you did nothing that will prevent that (the only way > to lock against hash_page is really an IPI & wait or to take the PTE's > busy and make them !present or something). So as far as I can tell, > a concurrent hash_page can still sneak into the hash some "small" > entries after you have supposedly flushed them.
Note that the _PAGE_PRESENT bit is removed eventually ... but much later, in __collapse_huge_page_copy() which will also flush the hash, so at least we will remove a stale hash entry that would have been added by the race above I suppose... but: - _PAGE_ACCESSED can still potentially be set after it was supposed to be stable - The clearing happens *after* copy_user_highpage(), ie, unless I missed something here, we potentially still have something writing to the 4k page while it's being copied, which is BAD. Now, let me know if I did miss something here :-) Cheers, Ben. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
