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authorJan Kara <jack@suse.cz>2018-12-28 11:39:12 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2018-12-28 23:11:51 +0300
commit89cb0888ca1483ad72648844ddd1b801863a8949 (patch)
tree63b626652f16c12b700c74eff2527a37d36fab61
parent84ade7c15ccfb46f852f4e2469b007a33651904d (diff)
downloadlinux-89cb0888ca1483ad72648844ddd1b801863a8949.tar.xz
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. [akpm@linux-foundation.org: remove EXPORT_SYMBOL(buffer_migrate_page_norefs)] Link: http://lkml.kernel.org/r/20181211172143.7358-5-jack@suse.cz Signed-off-by: Jan Kara <jack@suse.cz> Acked-by: Mel Gorman <mgorman@suse.de> Cc: Michal Hocko <mhocko@suse.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/fs.h4
-rw-r--r--mm/migrate.c60
2 files changed, 57 insertions, 7 deletions
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 26a8607b3c3c..1cda6648a41f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3269,8 +3269,12 @@ extern int generic_check_addressable(unsigned, u64);
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 *);
diff --git a/mm/migrate.c b/mm/migrate.c
index 8392140fb298..8dd57601714f 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -743,13 +743,9 @@ static bool buffer_migrate_lock_buffers(struct buffer_head *head,
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_space *mapping,
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 +826,30 @@ 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);
+}
#endif
/*