linux-kernel - [RFC PATCH 1/4] mm: Have the mempolicy pagewalk to avoid positive callback return codes

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Date:   Thu, 10 Oct 2019 15:40:55 +0200
From:   Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        torvalds@...ux-foundation.org, kirill@...temov.name
Cc:     Thomas Hellstrom <thellstrom@...are.com>
Subject: [RFC PATCH 1/4] mm: Have the mempolicy pagewalk to avoid positive callback return codes

From: Linus Torvalds <torvalds@...ux-foundation.org>

The pagewalk code is being reworked to have positive callback return codes
do walk control. Avoid using positive return codes: "1" is replaced by
"-EBUSY".

Co-developed-by: Thomas Hellstrom <thellstrom@...are.com>
Signed-off-by: Thomas Hellstrom <thellstrom@...are.com>
---
 mm/mempolicy.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 4ae967bcf954..df34c7498c27 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -482,8 +482,8 @@ static int queue_pages_pmd(pmd_t *pmd, spinlock_t *ptl, unsigned long addr,
  *
  * queue_pages_pte_range() has three possible return values:
  * 0 - pages are placed on the right node or queued successfully.
- * 1 - there is unmovable page, and MPOL_MF_MOVE* & MPOL_MF_STRICT were
- *     specified.
+ * -EBUSY - there is unmovable page, and MPOL_MF_MOVE* & MPOL_MF_STRICT were
+ *          specified.
  * -EIO - only MPOL_MF_STRICT was specified and an existing page was already
  *        on a node that does not follow the policy.
  */
@@ -503,7 +503,7 @@ static int queue_pages_pte_range(pmd_t *pmd, unsigned long addr,
 	if (ptl) {
 		ret = queue_pages_pmd(pmd, ptl, addr, end, walk);
 		if (ret != 2)
-			return ret;
+			return (ret == 1) ? -EBUSY : ret;
 	}
 	/* THP was split, fall through to pte walk */
 
@@ -546,7 +546,7 @@ static int queue_pages_pte_range(pmd_t *pmd, unsigned long addr,
 	cond_resched();
 
 	if (has_unmovable)
-		return 1;
+		return -EBUSY;
 
 	return addr != end ? -EIO : 0;
 }
@@ -669,9 +669,9 @@ static const struct mm_walk_ops queue_pages_walk_ops = {
  * passed via @private.
  *
  * queue_pages_range() has three possible return values:
- * 1 - there is unmovable page, but MPOL_MF_MOVE* & MPOL_MF_STRICT were
- *     specified.
  * 0 - queue pages successfully or no misplaced page.
+ * -EBUSY - there is unmovable page, but MPOL_MF_MOVE* & MPOL_MF_STRICT were
+ *	    specified.
  * -EIO - there is misplaced page and only MPOL_MF_STRICT was specified.
  */
 static int
@@ -1285,7 +1285,7 @@ static long do_mbind(unsigned long start, unsigned long len,
 	ret = queue_pages_range(mm, start, end, nmask,
 			  flags | MPOL_MF_INVERT, &pagelist);
 
-	if (ret < 0) {
+	if (ret < 0 && ret != -EBUSY) {
 		err = -EIO;
 		goto up_out;
 	}
@@ -1303,7 +1303,7 @@ static long do_mbind(unsigned long start, unsigned long len,
 				putback_movable_pages(&pagelist);
 		}
 
-		if ((ret > 0) || (nr_failed && (flags & MPOL_MF_STRICT)))
+		if ((ret < 0) || (nr_failed && (flags & MPOL_MF_STRICT)))
 			err = -EIO;
 	} else
 		putback_movable_pages(&pagelist);
-- 
2.21.0