Merge tag 'netfs-fixes-20211207' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull netfslib fixes from David Howells:

 - Fix a lockdep warning and potential deadlock. This is takes the
   simple approach of offloading the write-to-cache done from within a
   network filesystem read to a worker thread to avoid taking the
   sb_writer lock from the cache backing filesystem whilst holding the
   mmap lock on an inode from the network filesystem.

   Jan Kara posits a scenario whereby this can cause deadlock[1], though
   it's quite complex and I think requires someone in userspace to
   actually do I/O on the cache files. Matthew Wilcox isn't so certain,
   though[2].

   An alternative way to fix this, suggested by Darrick Wong, might be
   to allow cachefiles to prevent userspace from performing I/O upon the
   file - something like an exclusive open - but that's beyond the scope
   of a fix here if we do want to make such a facility in the future.

 - In some of the error handling paths where netfs_ops->cleanup() is
   called, the arguments are transposed[3]. gcc doesn't complain because
   one of the parameters is void* and one of the values is void*.

Link: https://lore.kernel.org/r/[email protected]/ [1]
Link: https://lore.kernel.org/r/Ya9eDiFCE2fO7K/[email protected]/ [2]
Link: https://lore.kernel.org/r/[email protected]/ [3]

* tag 'netfs-fixes-20211207' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  netfs: fix parameter of cleanup()
  netfs: Fix lockdep warning from taking sb_writers whilst holding mmap_lock

Author: torvalds

fs/netfs/read_helper.c

@@ -354,16 +354,11 @@ static void netfs_rreq_write_to_cache_work(struct work_struct *work)
 	netfs_rreq_do_write_to_cache(rreq);
 }
 
-static void netfs_rreq_write_to_cache(struct netfs_read_request *rreq,
-				      bool was_async)
+static void netfs_rreq_write_to_cache(struct netfs_read_request *rreq)
 {
-	if (was_async) {
-		rreq->work.func = netfs_rreq_write_to_cache_work;
-		if (!queue_work(system_unbound_wq, &rreq->work))
-			BUG();
-	} else {
-		netfs_rreq_do_write_to_cache(rreq);
-	}
+	rreq->work.func = netfs_rreq_write_to_cache_work;
+	if (!queue_work(system_unbound_wq, &rreq->work))
+		BUG();
 }
 
 /*
@@ -558,7 +553,7 @@ static void netfs_rreq_assess(struct netfs_read_request *rreq, bool was_async)
 	wake_up_bit(&rreq->flags, NETFS_RREQ_IN_PROGRESS);
 
 	if (test_bit(NETFS_RREQ_WRITE_TO_CACHE, &rreq->flags))
-		return netfs_rreq_write_to_cache(rreq, was_async);
+		return netfs_rreq_write_to_cache(rreq);
 
 	netfs_rreq_completed(rreq, was_async);
 }
@@ -960,7 +955,7 @@ int netfs_readpage(struct file *file,
 	rreq = netfs_alloc_read_request(ops, netfs_priv, file);
 	if (!rreq) {
 		if (netfs_priv)
-			ops->cleanup(netfs_priv, folio_file_mapping(folio));
+			ops->cleanup(folio_file_mapping(folio), netfs_priv);
 		folio_unlock(folio);
 		return -ENOMEM;
 	}
@@ -1191,7 +1186,7 @@ int netfs_write_begin(struct file *file, struct address_space *mapping,
 		goto error;
 have_folio_no_wait:
 	if (netfs_priv)
-		ops->cleanup(netfs_priv, mapping);
+		ops->cleanup(mapping, netfs_priv);
 	*_folio = folio;
 	_leave(" = 0");
 	return 0;
@@ -1202,7 +1197,7 @@ int netfs_write_begin(struct file *file, struct address_space *mapping,
 	folio_unlock(folio);
 	folio_put(folio);
 	if (netfs_priv)
-		ops->cleanup(netfs_priv, mapping);
+		ops->cleanup(mapping, netfs_priv);
 	_leave(" = %d", ret);
 	return ret;
 }