Commit 2990c89d authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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/20210922110420.GA21576@quack2.suse.cz/ [1]
Link: https://lore.kernel.org/r/Ya9eDiFCE2fO7K/S@casper.infradead.org/ [2]
Link: https://lore.kernel.org/r/20211207031449.100510-1-jefflexu@linux.alibaba.com/ [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
parents 3a49cc22 3cfef1b6

fs/netfs/read_helper.c

+8 −13
Original line number Diff line number Diff line
@@ -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);

	}

}



/*
@@ -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;

}