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