[Bug 209158] node / npm triggering zfs rename deadlock

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=209158

--- Comment #40 from commit-hook at freebsd.org ---
A commit references this bug:

Author: avg
Date: Thu Aug 11 20:48:04 UTC 2016
New revision: 303970
URL: https://svnweb.freebsd.org/changeset/base/303970

Log:
  MFC r303763,303791,303869: zfs: honour and make use of vfs vnode locking
protocol

  ZFS POSIX Layer is originally written for Solaris VFS which is very
  different from FreeBSD VFS.  Most importantly many things that FreeBSD VFS
  manages on behalf of all filesystems are implemented in ZPL in a different
  way.
  Thus, ZPL contains code that is redundant on FreeBSD or duplicates VFS
  functionality or, in the worst cases, badly interacts / interferes
  with VFS.

  The most prominent problem is a deadlock caused by the lock order reversal
  of vnode locks that may happen with concurrent zfs_rename() and lookup().
  The deadlock is a result of zfs_rename() not observing the vnode locking
  contract expected by VFS.

  This commit removes all ZPL internal locking that protects parent-child
  relationships of filesystem nodes.  These relationships are protected
  by vnode locks and the code is changed to take advantage of that fact
  and to properly interact with VFS.

  Removal of the internal locking allowed all ZPL dmu_tx_assign calls to
  use TXG_WAIT mode.

  Another victim, disputable perhaps, is ZFS support for filesystems with
  mixed case sensitivity.  That support is not provided by the OS anyway,
  so in ZFS it was a buch of dead code.

  To do:
  - replace ZFS_ENTER mechanism with VFS managed / visible mechanism
  - replace zfs_zget with zfs_vget[f] as much as possible
  - get rid of not really useful now zfs_freebsd_* adapters
  - more cleanups of unneeded / unused code
  - fix / replace .zfs support

  PR:           209158
  Approved by:  re (gjb)

Changes:
_U  stable/11/
  stable/11/sys/cddl/compat/opensolaris/sys/vnode.h
  stable/11/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_dir.h
  stable/11/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_vfsops.h
  stable/11/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_znode.h
  stable/11/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_acl.c
  stable/11/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_dir.c
  stable/11/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_sa.c
  stable/11/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vfsops.c
  stable/11/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c
  stable/11/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_znode.c

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