The patch titled
Subject: mm: migrate: provide buffer_migrate_page_norefs()
has been added to the -mm tree. Its filename is
mm-migrate-provide-buffer_migrate_page_norefs.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-migrate-provide-buffer_migrate_page_norefs.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-migrate-provide-buffer_migrate_page_norefs.patch
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------------------------------------------------------
From: Jan Kara <jack@xxxxxxx>
Subject: mm: migrate: provide buffer_migrate_page_norefs()
Provide a variant of buffer_migrate_page() that also checks whether there
are no unexpected references to buffer heads. This function will then be
safe to use for block device pages.
Link: http://lkml.kernel.org/r/20181211172143.7358-5-jack@xxxxxxx
Signed-off-by: Jan Kara <jack@xxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/include/linux/fs.h~mm-migrate-provide-buffer_migrate_page_norefs
+++ a/include/linux/fs.h
@@ -3264,8 +3264,12 @@ extern int generic_check_addressable(uns
extern int buffer_migrate_page(struct address_space *,
struct page *, struct page *,
enum migrate_mode);
+extern int buffer_migrate_page_norefs(struct address_space *,
+ struct page *, struct page *,
+ enum migrate_mode);
#else
#define buffer_migrate_page NULL
+#define buffer_migrate_page_norefs NULL
#endif
extern int setattr_prepare(struct dentry *, struct iattr *);
--- a/mm/migrate.c~mm-migrate-provide-buffer_migrate_page_norefs
+++ a/mm/migrate.c
@@ -743,13 +743,9 @@ static bool buffer_migrate_lock_buffers(
return true;
}
-/*
- * Migration function for pages with buffers. This function can only be used
- * if the underlying filesystem guarantees that no other references to "page"
- * exist.
- */
-int buffer_migrate_page(struct address_space *mapping,
- struct page *newpage, struct page *page, enum migrate_mode mode)
+static int __buffer_migrate_page(struct address_space *mapping,
+ struct page *newpage, struct page *page, enum migrate_mode mode,
+ bool check_refs)
{
struct buffer_head *bh, *head;
int rc;
@@ -767,6 +763,33 @@ int buffer_migrate_page(struct address_s
if (!buffer_migrate_lock_buffers(head, mode))
return -EAGAIN;
+ if (check_refs) {
+ bool busy;
+ bool invalidated = false;
+
+recheck_buffers:
+ busy = false;
+ spin_lock(&mapping->private_lock);
+ bh = head;
+ do {
+ if (atomic_read(&bh->b_count)) {
+ busy = true;
+ break;
+ }
+ bh = bh->b_this_page;
+ } while (bh != head);
+ spin_unlock(&mapping->private_lock);
+ if (busy) {
+ if (invalidated) {
+ rc = -EAGAIN;
+ goto unlock_buffers;
+ }
+ invalidate_bh_lrus();
+ invalidated = true;
+ goto recheck_buffers;
+ }
+ }
+
rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);
if (rc != MIGRATEPAGE_SUCCESS)
goto unlock_buffers;
@@ -803,7 +826,31 @@ unlock_buffers:
return rc;
}
+
+/*
+ * Migration function for pages with buffers. This function can only be used
+ * if the underlying filesystem guarantees that no other references to "page"
+ * exist. For example attached buffer heads are accessed only under page lock.
+ */
+int buffer_migrate_page(struct address_space *mapping,
+ struct page *newpage, struct page *page, enum migrate_mode mode)
+{
+ return __buffer_migrate_page(mapping, newpage, page, mode, false);
+}
EXPORT_SYMBOL(buffer_migrate_page);
+
+/*
+ * Same as above except that this variant is more careful and checks that there
+ * are also no buffer head references. This function is the right one for
+ * mappings where buffer heads are directly looked up and referenced (such as
+ * block device mappings).
+ */
+int buffer_migrate_page_norefs(struct address_space *mapping,
+ struct page *newpage, struct page *page, enum migrate_mode mode)
+{
+ return __buffer_migrate_page(mapping, newpage, page, mode, true);
+}
+EXPORT_SYMBOL(buffer_migrate_page_norefs);
#endif
/*
_
Patches currently in -mm which might be from jack@xxxxxxx are
mm-migration-factor-out-code-to-compute-expected-number-of-page-references.patch
mm-migrate-lock-buffers-before-migrate_page_move_mapping.patch
mm-migrate-move-migrate_page_lock_buffers.patch
mm-migrate-provide-buffer_migrate_page_norefs.patch
blkdev-avoid-migration-stalls-for-blkdev-pages.patch
mm-migrate-drop-unused-argument-of-migrate_page_move_mapping.patch
