[SRU][Pull][Bionic] Fix deadlock in ceph

[Connor Kuehl]

BugLink: https://bugs.launchpad.net/bugs/1834235

[Impact]

Deadlock may occur if iput_final() decides to wait for readahead pages 
while a lock is held.

In order to resolve this, the following two patches install an 
asynchronous "iput" for the ceph inodes so that a hold-and-wait deadlock 
doesn't occur. A more detailed example is shown in the original patch: 
https://github.com/ceph/ceph-client/commit/093ea205acd4b047cf5aacabc0c6ffecf198d2a9

Requested patches:

3e1d0452edcee ceph: avoid iput_final() while holding mutex or in dispatch thread
1cf89a8dee5e6 ceph: single workqueue for inode related works

[Test Case]

These changes were tested by the original requester with positive results over a few
days in their own environment where they first experienced the regression. They have
determined they are no longer experiencing the regression with this patch set applied
to a test kernel.

[Regression Potential] 

Several patches were required in order to cleanly cherry pick the requested patches.
A large number of changes increases the regression potential, however, these 
pre-requisite patches have been in mainline since early 2018 and the blast radius
is localized only to ceph.

----------------------------------------------------------------

The following changes since commit bb936a8a0dbbc727533e953071862a228044fa9f:

  block/bio: Do not zero user pages (2019-06-28 18:27:34 +0200)

are available in the Git repository at:

  git+ssh://connork@git.launchpad.net/~connork/+git/bionic ceph

for you to fetch changes up to 4a7619c37800ae7433f2bd5e2d66ce4a3c60d23e:

  ceph: avoid iput_final() while holding mutex or in dispatch thread (2019-06-28 09:32:06 -0700)

----------------------------------------------------------------
Luis Henriques (6):
      ceph: quota: add initial infrastructure to support cephfs quotas
      ceph: quota: support for ceph.quota.max_files
      ceph: quota: don't allow cross-quota renames
      ceph: quota: support for ceph.quota.max_bytes
      ceph: quota: update MDS when max_bytes is approaching
      ceph: quota: add counter for snaprealms with quota

Yan, Zheng (8):
      ceph: use atomic_t for ceph_inode_info::i_shared_gen
      ceph: define argument structure for handle_cap_grant
      ceph: flush pending works before shutdown super
      ceph: send cap releases more aggressively
      ceph: single workqueue for inode related works
      ceph: avoid dereferencing invalid pointer during cached readdir
      ceph: fix root quota realm check
      ceph: avoid iput_final() while holding mutex or in dispatch thread

 Documentation/filesystems/ceph.txt |  12 ++
 fs/ceph/Makefile                   |   2 +-
 fs/ceph/caps.c                     | 154 ++++++++++---------
 fs/ceph/dir.c                      |  75 +++++++---
 fs/ceph/file.c                     |  23 ++-
 fs/ceph/inode.c                    | 211 ++++++++++++++++----------
 fs/ceph/mds_client.c               | 113 +++++++++++---
 fs/ceph/mds_client.h               |  14 +-
 fs/ceph/quota.c                    | 298 +++++++++++++++++++++++++++++++++++++
 fs/ceph/snap.c                     |  16 +-
 fs/ceph/super.c                    |  38 ++---
 fs/ceph/super.h                    |  62 ++++++--
 fs/ceph/xattr.c                    |  44 ++++++
 include/linux/ceph/ceph_features.h |   1 +
 include/linux/ceph/ceph_fs.h       |  17 +++
 net/ceph/ceph_common.c             |   1 +
 16 files changed, 847 insertions(+), 234 deletions(-)
 create mode 100644 fs/ceph/quota.c

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