[PATCH] thp: document barrier() in wrprotect THP fault path

[Andrea Arcangeli]

Inline doc.

Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
---
 mm/memory.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 420a449..9ec5bba 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3522,6 +3522,12 @@ retry:
 		pmd_t orig_pmd = *pmd;
 		int ret;
 
+		/*
+		 * flush orig_pmd on the stack to avoid invalidating
+		 * the pmd_trans_huge(orig_pmd) check and to allow
+		 * do_huge_pmd_wp_page to run a reliable
+		 * pmd_same(*pmd, orig_pmd).
+		 */
 		barrier();
 		if (pmd_trans_huge(orig_pmd)) {
 			if (flags & FAULT_FLAG_WRITE &&
--
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