fs/cachefiles: Remove wait_bit_key layout dependency

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

A comment on the need to maintain structure layout equivalence was added by
Linus[1] and that is no longer applicable.

Fixes: 62906027091f ("mm: add PageWaiters indicating tasks are waiting for a page bit")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: kafs-testing@auristor.com
cc: linux-cachefs@redhat.com
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/20210320054104.1300774-2-willy@infradead.org/
Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3510ca20ece0150af6b10c77a74ff1b5c198e3e2

diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c
index e027c71..8ffc40e 100644 (file)
--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -24,17 +24,16 @@ 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 wait_page_key *key = _key;
        struct page *page = wait->private;
 
        ASSERT(key);
 
        _enter("{%lu},%u,%d,{%p,%u}",
               monitor->netfs_page->index, mode, sync,
-              key->flags, key->bit_nr);
+              key->page, key->bit_nr);
 
-       if (key->flags != &page->flags ||
-           key->bit_nr != PG_locked)
+       if (key->page != page || key->bit_nr != PG_locked)
                return 0;
 
        _debug("--- monitor %p %lx ---", page, page->flags);

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 20225b0..8f4daac 100644 (file)
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -559,7 +559,6 @@ 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 page *page;
        int bit_nr;