[PATCH v6 5/6] mm: use vma_start_write_killable() in process_vma_walk_lock()

[Suren Baghdasaryan]

Replace vma_start_write() with vma_start_write_killable() when
process_vma_walk_lock() is used with PGWALK_WRLOCK option.
Adjust its direct and indirect users to check for a possible error
and handle it. Ensure users handle EINTR correctly and do not ignore
it. When queue_pages_range() fails, check whether it failed due to
a fatal signal or some other reason and return appropriate error.

Suggested-by: Matthew Wilcox <willy at infradead.org>
Signed-off-by: Suren Baghdasaryan <surenb at google.com>
---
 fs/proc/task_mmu.c | 12 ++++++------
 mm/mempolicy.c     | 10 +++++++++-
 mm/pagewalk.c      | 22 +++++++++++++++-------
 3 files changed, 30 insertions(+), 14 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index e091931d7ca1..33e5094a7842 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1774,15 +1774,15 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
 	struct vm_area_struct *vma;
 	enum clear_refs_types type;
 	int itype;
-	int rv;
+	int err;
 
 	if (count > sizeof(buffer) - 1)
 		count = sizeof(buffer) - 1;
 	if (copy_from_user(buffer, buf, count))
 		return -EFAULT;
-	rv = kstrtoint(strstrip(buffer), 10, &itype);
-	if (rv < 0)
-		return rv;
+	err = kstrtoint(strstrip(buffer), 10, &itype);
+	if (err)
+		return err;
 	type = (enum clear_refs_types)itype;
 	if (type < CLEAR_REFS_ALL || type >= CLEAR_REFS_LAST)
 		return -EINVAL;
@@ -1824,7 +1824,7 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
 						0, mm, 0, -1UL);
 			mmu_notifier_invalidate_range_start(&range);
 		}
-		walk_page_range(mm, 0, -1, &clear_refs_walk_ops, &cp);
+		err = walk_page_range(mm, 0, -1, &clear_refs_walk_ops, &cp);
 		if (type == CLEAR_REFS_SOFT_DIRTY) {
 			mmu_notifier_invalidate_range_end(&range);
 			flush_tlb_mm(mm);
@@ -1837,7 +1837,7 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
 	}
 	put_task_struct(task);
 
-	return count;
+	return err ? : count;
 }
 
 const struct file_operations proc_clear_refs_operations = {
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index c38a90487531..51f298cfc33b 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -969,6 +969,7 @@ static const struct mm_walk_ops queue_pages_lock_vma_walk_ops = {
  *      (a hugetlbfs page or a transparent huge page being counted as 1).
  * -EIO - a misplaced page found, when MPOL_MF_STRICT specified without MOVEs.
  * -EFAULT - a hole in the memory range, when MPOL_MF_DISCONTIG_OK unspecified.
+ * -EINTR - walk got terminated due to pending fatal signal.
  */
 static long
 queue_pages_range(struct mm_struct *mm, unsigned long start, unsigned long end,
@@ -1545,7 +1546,14 @@ static long do_mbind(unsigned long start, unsigned long len,
 			flags | MPOL_MF_INVERT | MPOL_MF_WRLOCK, &pagelist);
 
 	if (nr_failed < 0) {
-		err = nr_failed;
+		/*
+		 * queue_pages_range() might override the original error with -EFAULT.
+		 * Confirm that fatal signals are still treated correctly.
+		 */
+		if (fatal_signal_pending(current))
+			err = -EINTR;
+		else
+			err = nr_failed;
 		nr_failed = 0;
 	} else {
 		vma_iter_init(&vmi, mm, start);
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 3ae2586ff45b..eca7bc711617 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -443,14 +443,13 @@ static inline void process_mm_walk_lock(struct mm_struct *mm,
 		mmap_assert_write_locked(mm);
 }
 
-static inline void process_vma_walk_lock(struct vm_area_struct *vma,
-					 enum page_walk_lock walk_lock)
+static int process_vma_walk_lock(struct vm_area_struct *vma,
+				 enum page_walk_lock walk_lock)
 {
 #ifdef CONFIG_PER_VMA_LOCK
 	switch (walk_lock) {
 	case PGWALK_WRLOCK:
-		vma_start_write(vma);
-		break;
+		return vma_start_write_killable(vma);
 	case PGWALK_WRLOCK_VERIFY:
 		vma_assert_write_locked(vma);
 		break;
@@ -462,6 +461,7 @@ static inline void process_vma_walk_lock(struct vm_area_struct *vma,
 		break;
 	}
 #endif
+	return 0;
 }
 
 /*
@@ -505,7 +505,9 @@ int walk_page_range_mm_unsafe(struct mm_struct *mm, unsigned long start,
 			if (ops->pte_hole)
 				err = ops->pte_hole(start, next, -1, &walk);
 		} else { /* inside vma */
-			process_vma_walk_lock(vma, ops->walk_lock);
+			err = process_vma_walk_lock(vma, ops->walk_lock);
+			if (err)
+				break;
 			walk.vma = vma;
 			next = min(end, vma->vm_end);
 			vma = find_vma(mm, vma->vm_end);
@@ -722,6 +724,7 @@ int walk_page_range_vma_unsafe(struct vm_area_struct *vma, unsigned long start,
 		.vma		= vma,
 		.private	= private,
 	};
+	int err;
 
 	if (start >= end || !walk.mm)
 		return -EINVAL;
@@ -729,7 +732,9 @@ int walk_page_range_vma_unsafe(struct vm_area_struct *vma, unsigned long start,
 		return -EINVAL;
 
 	process_mm_walk_lock(walk.mm, ops->walk_lock);
-	process_vma_walk_lock(vma, ops->walk_lock);
+	err = process_vma_walk_lock(vma, ops->walk_lock);
+	if (err)
+		return err;
 	return __walk_page_range(start, end, &walk);
 }
 
@@ -752,6 +757,7 @@ int walk_page_vma(struct vm_area_struct *vma, const struct mm_walk_ops *ops,
 		.vma		= vma,
 		.private	= private,
 	};
+	int err;
 
 	if (!walk.mm)
 		return -EINVAL;
@@ -759,7 +765,9 @@ int walk_page_vma(struct vm_area_struct *vma, const struct mm_walk_ops *ops,
 		return -EINVAL;
 
 	process_mm_walk_lock(walk.mm, ops->walk_lock);
-	process_vma_walk_lock(vma, ops->walk_lock);
+	err = process_vma_walk_lock(vma, ops->walk_lock);
+	if (err)
+		return err;
 	return __walk_page_range(vma->vm_start, vma->vm_end, &walk);
 }
 
-- 
2.53.0.1018.g2bb0e51243-goog