mm/hmm: Simplify hmm_get_or_create and make it reliable

As coded this function can false-fail in various racy situations. Make it
reliable and simpler by running under the write side of the mmap_sem and
avoiding the false-failing compare/exchange pattern. Due to the mmap_sem
this no longer has to avoid racing with a 2nd parallel
hmm_get_or_create().

Unfortunately this still has to use the page_table_lock as the
non-sleeping lock protecting mm->hmm, since the contexts where we free the
hmm are incompatible with mmap_sem.

Signed-off-by: Jason Gunthorpe <[email protected]>
Reviewed-by: John Hubbard <[email protected]>
Reviewed-by: Ralph Campbell <[email protected]>
Reviewed-by: Ira Weiny <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Tested-by: Philip Yang <[email protected]>

0 files changed, 0 insertions, 0 deletions