Linux 3.16.38

[Ben Hutchings]

I'm announcing the release of the 3.16.38 kernel.

All users of the 3.16 kernel series should upgrade.

The updated 3.16.y git tree can be found at:
        https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git linux-3.16.y
and can be browsed at the normal kernel.org git web browser:
        https://git.kernel.org/?p=linux/kernel/git/stable/linux-stable.git

The diff from 3.16.37 is attached to this message.

Ben.

------------

 Makefile           |  2 +-
 include/linux/mm.h |  1 +
 mm/gup.c           | 14 ++++++++++++--
 3 files changed, 14 insertions(+), 3 deletions(-)

Ben Hutchings (1):
      Linux 3.16.38

Linus Torvalds (1):
      mm: remove gup_flags FOLL_WRITE games from __get_user_pages()

diff --git a/Makefile b/Makefile
index e49d13717d31..37083fbc8784 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 VERSION = 3
 PATCHLEVEL = 16
-SUBLEVEL = 37
+SUBLEVEL = 38
 EXTRAVERSION =
 NAME = Museum of Fishiegoodies
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7ac72a725798..e648c24e8410 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2007,6 +2007,7 @@ static inline struct page *follow_page(struct vm_area_struct *vma,
 #define FOLL_HWPOISON	0x100	/* check page is hwpoisoned */
 #define FOLL_NUMA	0x200	/* force NUMA hinting page fault */
 #define FOLL_MIGRATION	0x400	/* wait for page to replace migration entry */
+#define FOLL_COW	0x4000	/* internal GUP flag */
 
 typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
 			void *data);
diff --git a/mm/gup.c b/mm/gup.c
index 9cb1cfbe4677..2e4b9873b5aa 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -28,6 +28,16 @@ static struct page *no_page_table(struct vm_area_struct *vma,
 	return NULL;
 }
 
+/*
+ * FOLL_FORCE can write to even unwritable pte's, but only
+ * after we've gone through a COW cycle and they are dirty.
+ */
+static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
+{
+	return pte_write(pte) ||
+		((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
+}
+
 static struct page *follow_page_pte(struct vm_area_struct *vma,
 		unsigned long address, pmd_t *pmd, unsigned int flags)
 {
@@ -62,7 +72,7 @@ retry:
 	}
 	if ((flags & FOLL_NUMA) && pte_numa(pte))
 		goto no_page;
-	if ((flags & FOLL_WRITE) && !pte_write(pte)) {
+	if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags)) {
 		pte_unmap_unlock(ptep, ptl);
 		return NULL;
 	}
@@ -302,7 +312,7 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 	 * reCOWed by userspace write).
 	 */
 	if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE))
-		*flags &= ~FOLL_WRITE;
+	        *flags |= FOLL_COW;
 	return 0;
 }

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