Messages in this thread | | | Date | Tue, 13 May 2003 16:20:38 -0700 | From | William Lee Irwin III <> | Subject | Re: Race between vmtruncate and mapped areas? |
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On Tuesday, May 13, 2003 16:11:39 -0700 William Lee Irwin III <wli@holomorphy.com> wrote: >> Okay, what's stopping filemap_nopage() from fetching the page from >> pagecache after one of the mm->mmap_sem's is dropped but before >> truncate_inode_pages() removes the page? The fault path is only locked >> out for one mm during one part of the operation. I can see taking >> ->i_sem in do_no_page() fixing it, but not ->mmap_sem in vmtruncate() >> (but of course that's _far_ too heavy-handed to merge at all).
On Tue, May 13, 2003 at 06:16:16PM -0500, Dave McCracken wrote: > mmap_sem is held for read across the entire fault, so by the time > vmtruncate_list() can call zap_page_range() the page has been instantiated > in the page table and will get removed.
That's not quite the answer, inode->i_size is.
The mmap_sem works because then ->i_size can't be sampled by filemap_nopage() before the pagetable wiping operation starts.
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