linux-kernel - [PATCH 5.10 210/221] fs/cachefiles: Remove wait_bit

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Date:   Mon, 29 Mar 2021 09:59:01 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Christoph Hellwig <hch@....de>,
        David Howells <dhowells@...hat.com>, kafs-testing@...istor.com,
        linux-cachefs@...hat.com, linux-mm@...ck.org
Subject: [PATCH 5.10 210/221] fs/cachefiles: Remove wait_bit_key layout dependency

From: Matthew Wilcox (Oracle) <willy@...radead.org>

commit 39f985c8f667c80a3d1eb19d31138032fa36b09e upstream.

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Linus[1] and that is no longer applicable.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@...radead.org>
Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: David Howells <dhowells@...hat.com>
Tested-by: kafs-testing@...istor.com
cc: linux-cachefs@...hat.com
cc: linux-mm@...ck.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 [1]
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/cachefiles/rdwr.c    |    7 +++----
 include/linux/pagemap.h |    1 -
 2 files changed, 3 insertions(+), 5 deletions(-)

--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -24,17 +24,16 @@ static int cachefiles_read_waiter(wait_q
 		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);
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -559,7 +559,6 @@ static inline pgoff_t linear_page_index(
 	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;