[v4,25/25] cachefiles: Switch to wait_page_key

Commit Message

Matthew Wilcox March 5, 2021, 4:19 a.m. UTC

Cachefiles was relying on wait_page_key and wait_bit_key being the
same layout, which is fragile.  Now that wait_page_key is exposed in
the pagemap.h header, we can remove that fragility.  Also switch it
to use the folio directly instead of the page.

Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
---
 fs/cachefiles/rdwr.c    | 13 ++++++-------
 include/linux/pagemap.h |  1 -
 2 files changed, 6 insertions(+), 8 deletions(-)

Comments

Christoph Hellwig March 17, 2021, 5:45 p.m. UTC | #1

On Fri, Mar 05, 2021 at 04:19:01AM +0000, Matthew Wilcox (Oracle) wrote:
> Cachefiles was relying on wait_page_key and wait_bit_key being the
> same layout, which is fragile.  Now that wait_page_key is exposed in
> the pagemap.h header, we can remove that fragility.  Also switch it
> to use the folio directly instead of the page.

Yikes.  That fix itself is something that should go into mainline ASAP as
it fixes a massive landmine instead of mixing it up with the folio
conversion.

Patch

diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c
index e027c718ca01..b1dbc484a9c7 100644
--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -24,22 +24,21 @@  static int cachefiles_read_waiter(wait_queue_entry_t *wait, unsigned mode,
 		container_of(wait, struct cachefiles_one_read, monitor);
 	struct cachefiles_object *object;
 	struct fscache_retrieval *op = monitor->op;
-	struct wait_bit_key *key = _key;
-	struct page *page = wait->private;
+	struct wait_page_key *key = _key;
+	struct folio *folio = wait->private;
 
 	ASSERT(key);
 
 	_enter("{%lu},%u,%d,{%p,%u}",
 	       monitor->netfs_page->index, mode, sync,
-	       key->flags, key->bit_nr);
+	       key->folio, key->bit_nr);
 
-	if (key->flags != &page->flags ||
-	    key->bit_nr != PG_locked)
+	if (key->folio != folio || key->bit_nr != PG_locked)
 		return 0;
 
-	_debug("--- monitor %p %lx ---", page, page->flags);
+	_debug("--- monitor %p %lx ---", folio, folio->page.flags);
 
-	if (!PageUptodate(page) && !PageError(page)) {
+	if (!FolioUptodate(folio) && !FolioError(folio)) {
 		/* unlocked, not uptodate and not erronous? */
 		_debug("page probably truncated");
 	}
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 2236f726bf01..699a6a0bcc54 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -609,7 +609,6 @@  static inline pgoff_t linear_page_index(struct vm_area_struct *vma,
 	return pgoff;
 }
 
-/* This has the same layout as wait_bit_key - see fs/cachefiles/rdwr.c */
 struct wait_page_key {
 	struct folio *folio;
 	int bit_nr;