Merge branch 'for-jens' of git://git.drbd.org/linux-drbd into for-3.6/drivers

1 files changed, 10 insertions, 0 deletions

diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 6f2b45a9b6bc..ff4947b7a976 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -484,6 +484,16 @@ static inline int pmd_none_or_trans_huge_or_clear_bad(pmd_t *pmd)
         /*
          * The barrier will stabilize the pmdval in a register or on
          * the stack so that it will stop changing under the code.
+         *
+         * When CONFIG_TRANSPARENT_HUGEPAGE=y on x86 32bit PAE,
+         * pmd_read_atomic is allowed to return a not atomic pmdval
+         * (for example pointing to an hugepage that has never been
+         * mapped in the pmd). The below checks will only care about
+         * the low part of the pmd with 32bit PAE x86 anyway, with the
+         * exception of pmd_none(). So the important thing is that if
+         * the low part of the pmd is found null, the high part will
+         * be also null or the pmd_none() check below would be
+         * confused.
          */
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
         barrier();