Re: [PATCH] Remove page_table_lock from vma manipulations

[William Lee Irwin III]

On Wed, Jun 04, 2003 at 05:30:25PM -0500, Dave McCracken wrote:
> After more careful consideration, I don't see any reasons why
> page_table_lock is necessary for dealing with vmas.  I found one spot in
> swapoff, but it was easily changed to mmap_sem.  I've beat on this code and
> mjb has beat on this code with no problems.  Here's the patch to remove it.
> Feel free to poke holes in it.

shrink_list() calls try_to_unmap() under pte_chain_lock(page), and
hence try_to_unmap() cannot sleep. Furthermore try_to_unmap() calls
find_vma() under the sole protection of
spin_trylock(&mm->page_table_lock), which I don't see changed to a
read_trylock(&mm->mmap_sem) here.

Hence, this is racy.

-- wli