Merge tag 'afs-cachefiles-fixes-20210323' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull cachefiles and afs fixes from David Howells:
 "Fixes from Matthew Wilcox for page waiting-related issues in
  cachefiles and afs as extracted from his folio series[1]:

   - In cachefiles, remove the use of the wait_bit_key struct to access
     something that's actually in wait_page_key format. The proper
     struct is now available in the header, so that should be used
     instead.

   - Add a proper wait function for waiting killably on the page
     writeback flag. This includes a recent bugfix[2] that's not in the
     afs code.

   - In afs, use the function added in (2) rather than using
     wait_on_page_bit_killable() which doesn't provide the
     aforementioned bugfix"

Link: https://lore.kernel.org/r/20210320054104.1300774-1-willy@infradead.org[1]
Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c2407cf7d22d0c0d94cf20342b3b8f06f1d904e7 [2]
Link: https://lore.kernel.org/r/20210323120829.GC1719932@casper.infradead.org/ # v1

* tag 'afs-cachefiles-fixes-20210323' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  afs: Use wait_on_page_writeback_killable
  mm/writeback: Add wait_on_page_writeback_killable
  fs/cachefiles: Remove wait_bit_key layout dependency

Author: torvalds

fs/afs/write.c

@@ -851,8 +851,7 @@ vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
 	fscache_wait_on_page_write(vnode->cache, vmf->page);
 #endif
 
-	if (PageWriteback(vmf->page) &&
-	    wait_on_page_bit_killable(vmf->page, PG_writeback) < 0)
+	if (wait_on_page_writeback_killable(vmf->page))
 		return VM_FAULT_RETRY;
 
 	if (lock_page_killable(vmf->page) < 0)

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);

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;
@@ -683,6 +682,7 @@ static inline int wait_on_page_locked_killable(struct page *page)
 
 int put_and_wait_on_page_locked(struct page *page, int state);
 void wait_on_page_writeback(struct page *page);
+int wait_on_page_writeback_killable(struct page *page);
 extern void end_page_writeback(struct page *page);
 void wait_for_stable_page(struct page *page);
 

mm/page-writeback.c

@@ -2833,6 +2833,22 @@ void wait_on_page_writeback(struct page *page)
 }
 EXPORT_SYMBOL_GPL(wait_on_page_writeback);
 
+/*
+ * Wait for a page to complete writeback.  Returns -EINTR if we get a
+ * fatal signal while waiting.
+ */
+int wait_on_page_writeback_killable(struct page *page)
+{
+	while (PageWriteback(page)) {
+		trace_wait_on_page_writeback(page, page_mapping(page));
+		if (wait_on_page_bit_killable(page, PG_writeback))
+			return -EINTR;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(wait_on_page_writeback_killable);
+
 /**
  * wait_for_stable_page() - wait for writeback to finish, if necessary.
  * @page:	The page to wait on.