Messages in this thread | | | Date | Wed, 7 Mar 2007 02:15:18 -0800 | From | Andrew Morton <> | Subject | Re: [patch 1/8] fix race in clear_page_dirty_for_io() |
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(cc's reinstated)
On Wed, 07 Mar 2007 09:09:50 +0100 Miklos Szeredi <miklos@szeredi.hu> wrote:
> There's a race in clear_page_dirty_for_io() that allows a page to have > cleared PG_dirty, while being mapped read-write into the page table(s).
I assume you refer to this:
* FIXME! We still have a race here: if somebody * adds the page back to the page tables in * between the "page_mkclean()" and the "TestClearPageDirty()", * we might have it mapped without the dirty bit set. */ if (page_mkclean(page)) set_page_dirty(page); if (TestClearPageDirty(page)) { dec_zone_page_state(page, NR_FILE_DIRTY); return 1; }
I guess the comment actually refers to a writefault after the set_page_dirty() and before the TestClearPageDirty(). The fault handler will run set_page_dirty() and will return to userspace to rerun the write. The page then gets set pte-dirty but this thread of control will now make the page !PageDirty() and will write it out.
With Nick's proposed lock-the-page-in-pagefaults patches, we have lock_page() synchronisation between pagefaults and clear_page_dirty_for_io() which I think will fix this.
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