tree 4db3cc908179a629b73dad093ca59797626ba645
parent c04517d59bea7a645bc60d1981ddb87625fb5ffa
author Mathieu Chartier <mathieuc@google.com> 1401480166 -0700
committer Mathieu Chartier <mathieuc@google.com> 1401489066 -0700

Fix race condition in MemMap::MapAnonymous.

Previously we were using MAP_FIXED which introduced a serious race
condition if MAP_32BIT was set since it would possibly overwrite
an existing map at the address which we determined was free with
msync. There was a window of time after we had msynced a page where
another thread could map something at that page. The new method
avoids using MAP_FIXED and unmaps allocations which succeed but
aren't in the low 4GB when MAP_32BIT is set.

Bug: 15338094
Bug: 14974497

(cherry picked from commit c355a2a78d6ebdfdb645221275affb9136b4c667)

Change-Id: I292a74dbf2ef5ddfb8d0524ae8bc1efbcbd106c8