Commit 89cb0888 authored by Jan Kara's avatar Jan Kara Committed by Linus Torvalds
Browse files

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: default avatarJan Kara <jack@suse.cz>
Acked-by: default avatarMel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 84ade7c1

include/linux/fs.h

+4 −0
Original line number Diff line number Diff line
@@ -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 *);

mm/migrate.c

+53 −7
Original line number Diff line number Diff line
@@ -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



/*

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