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. [akpm@xxxxxxxxxxxxxxxxxxxx: remove EXPORT_SYMBOL(buffer_migrate_page_norefs)] 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 @@ -3269,8 +3269,12 @@ 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 +826,30 @@ 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 /* _
