Re: Race between vmtruncate and mapped areas?

[Dave McCracken <dmccr@us.ibm.com>]

--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).

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.

Dave

======================================================================
Dave McCracken          IBM Linux Base Kernel Team      1-512-838-3059
dmccr@us.ibm.com                                        T/L   678-3059

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