Messages in this thread | | | Date | Tue, 13 May 2003 16:11:39 -0700 | From | William Lee Irwin III <> | Subject | Re: Race between vmtruncate and mapped areas? |
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On Tuesday, May 13, 2003 15:49:29 -0700 William Lee Irwin III <wli@holomorphy.com> wrote: >> That doesn't sound like it's going to help, there isn't a unique >> mmap_sem to be taken and so we just get caught between acquisitions >> with the same problem.
On Tue, May 13, 2003 at 06:00:08PM -0500, Dave McCracken wrote: > Actually it does fix it. I added code in vmtruncate_list() to do a > down_write(&vma->vm_mm->mmap_sem) around the zap_page_range(), and the > problem went away. It serializes against any outstanding page faults on a > particular page table. New faults will see that the page is no longer in > the file and fail with SIGBUS. Andrew's test case stopped failing. > I've attached the patch so you can see what I did. > Can anyone think of any gotchas to this solution?
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).
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