When quota is on, it is expected that unused quota inodes have a
value of NULLFSINO. The changes to support a separate project quota
in 3.12 broken this rule for non-project quota inode enabled
filesystem, as the code now refuses to write the group quota inode
if neither group or project quotas are enabled. This regression was
introduced by commit d892d58 ("xfs: Start using pquotaino from the
superblock").

In this case, we should be writing NULLFSINO rather than nothing to
ensure that we leave the group quota inode in a valid state while
quotas are enabled.

Failure to do so doesn't cause a current kernel to break - the
separate project quota inodes introduced translation code to always
treat a zero inode as NULLFSINO. This was introduced by commit
0102629 ("xfs: Initialize all quota inodes to be NULLFSINO") with is
also in 3.12 but older kernels do not do this and hence taking a
filesystem back to an older kernel can result in quotas failing
initialisation at mount time. When that happens, we see this in
dmesg:

[ 1649.215390] XFS (sdb): Mounting Filesystem
[ 1649.316894] XFS (sdb): Failed to initialize disk quotas.
[ 1649.316902] XFS (sdb): Ending clean mount

By ensuring that we write NULLFSINO to quota inodes that aren't
active, we avoid this problem. We have to be really careful when
determining if the quota inodes are active or not, because we don't
want to write a NULLFSINO if the quota inodes are active and we
simply aren't updating them.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

The allocation stack switch at xfs_bmapi_allocate() has served it's
purpose, but is no longer a sufficient solution to the stack usage
problem we have in the XFS allocation path.

Whilst the kernel stack size is now 16k, that is not a valid reason
for undoing all our "keep stack usage down" modifications. What it
does allow us to do is have the freedom to refine and perfect the
modifications knowing that if we get it wrong it won't blow up in
our faces - we have a safety net now.

This is important because we still have the issue of older kernels
having smaller stacks and that they are still supported and are
demonstrating a wide range of different stack overflows.  Red Hat
has several open bugs for allocation based stack overflows from
directory modifications and direct IO block allocation and these
problems still need to be solved. If we can solve them upstream,
then distro's won't need to bake their own unique solutions.

To that end, I've observed that every allocation based stack
overflow report has had a specific characteristic - it has happened
during or directly after a bmap btree block split. That event
requires a new block to be allocated to the tree, and so we
effectively stack one allocation stack on top of another, and that's
when we get into trouble.

A further observation is that bmap btree block splits are much rarer
than writeback allocation - over a range of different workloads I've
observed the ratio of bmap btree inserts to splits ranges from 100:1
(xfstests run) to 10000:1 (local VM image server with sparse files
that range in the hundreds of thousands to millions of extents).
Either way, bmap btree split events are much, much rarer than
allocation events.

Finally, we have to move the kswapd state to the allocation workqueue
work when allocation is done on behalf of kswapd. This is proving to
cause significant perturbation in performance under memory pressure
and appears to be generating allocation deadlock warnings under some
workloads, so avoiding the use of a workqueue for the majority of
kswapd writeback allocation will minimise the impact of such
behaviour.

Hence it makes sense to move the stack switch to xfs_btree_split()
and only do it for bmap btree splits. Stack switches during
allocation will be much rarer, so there won't be significant
performacne overhead caused by switching stacks. The worse case
stack from all allocation paths will be split, not just writeback.
And the majority of memory allocations will be done in the correct
context (e.g. kswapd) without causing additional latency, and so we
simplify the memory reclaim interactions between processes,
workqueues and kswapd.

The worst stack I've been able to generate with this patch in place
is 5600 bytes deep. It's very revealing because we exit XFS at:

37)     1768      64   kmem_cache_alloc+0x13b/0x170

about 1800 bytes of stack consumed, and the remaining 3800 bytes
(and 36 functions) is memory reclaim, swap and the IO stack. And
this occurs in the inode allocation from an open(O_CREAT) syscall,
not writeback.

The amount of stack being used is much less than I've previously be
able to generate - fs_mark testing has been able to generate stack
usage of around 7k without too much trouble; with this patch it's
only just getting to 5.5k. This is primarily because the metadata
allocation paths (e.g. directory blocks) are no longer causing
double splits on the same stack, and hence now stack tracing is
showing swapping being the worst stack consumer rather than XFS.

Performance of fs_mark inode create workloads is unchanged.
Performance of fs_mark async fsync workloads is consistently good
with context switches reduced by around 150,000/s (30%).
Performance of dbench, streaming IO and postmark is unchanged.
Allocation deadlock warnings have not been seen on the workloads
that generated them since adding this patch.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

This reverts commit 1f6d64829db78a7e1d63e15c9f48f0a5d2b5a679.

This commit resulted in regressions in performance in low
memory situations where kswapd was doing writeback of delayed
allocation blocks. It resulted in significant parallelism of the
kswapd work and with the special kswapd flags meant that hundreds of
active allocation could dip into kswapd specific memory reserves and
avoid being throttled. This cause a large amount of performance
variation, as well as random OOM-killer invocations that didn't
previously exist.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

Pull vfs updates from Al Viro:
 "This the bunch that sat in -next + lock_parent() fix.  This is the
  minimal set; there's more pending stuff.

  In particular, I really hope to get acct.c fixes merged this cycle -
  we need that to deal sanely with delayed-mntput stuff.  In the next
  pile, hopefully - that series is fairly short and localized
  (kernel/acct.c, fs/super.c and fs/namespace.c).  In this pile: more
  iov_iter work.  Most of prereqs for ->splice_write with sane locking
  order are there and Kent's dio rewrite would also fit nicely on top of
  this pile"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (70 commits)
  lock_parent: don't step on stale ->d_parent of all-but-freed one
  kill generic_file_splice_write()
  ceph: switch to iter_file_splice_write()
  shmem: switch to iter_file_splice_write()
  nfs: switch to iter_splice_write_file()
  fs/splice.c: remove unneeded exports
  ocfs2: switch to iter_file_splice_write()
  ->splice_write() via ->write_iter()
  bio_vec-backed iov_iter
  optimize copy_page_{to,from}_iter()
  bury generic_file_aio_{read,write}
  lustre: get rid of messing with iovecs
  ceph: switch to ->write_iter()
  ceph_sync_direct_write: stop poking into iov_iter guts
  ceph_sync_read: stop poking into iov_iter guts
  new helper: copy_page_from_iter()
  fuse: switch to ->write_iter()
  btrfs: switch to ->write_iter()
  ocfs2: switch to ->write_iter()
  xfs: switch to ->write_iter()
  ...

Backmerge of dcache.c changes from mainline.  It's that, or complete
rebase...

Conflicts:
	fs/splice.c

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

iter_file_splice_write() - a ->splice_write() instance that gathers the
pipe buffers, builds a bio_vec-based iov_iter covering those and feeds
it to ->write_iter().  A bunch of simple cases coverted to that...

[AV: fixed the braino spotted by Cyrill]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Pull xfs updates from Dave Chinner:
 "This update contains:
   - cleanup removing unused function args
   - rework of the filestreams allocator to use dentry cache parent
     lookups
   - new on-disk free inode btree and optimised inode allocator
   - various bug fixes
   - rework of internal attribute API
   - cleanup of superblock feature bit support to remove historic cruft
   - more fixes and minor cleanups
   - added a new directory/attribute geometry abstraction
   - yet more fixes and minor cleanups"

* tag 'xfs-for-linus-3.16-rc1' of git://oss.sgi.com/xfs/xfs: (86 commits)
  xfs: fix xfs_da_args sparse warning in xfs_readdir
  xfs: Fix rounding in xfs_alloc_fix_len()
  xfs: tone down writepage/releasepage WARN_ONs
  xfs: small cleanup in xfs_lowbit64()
  xfs: kill xfs_buf_geterror()
  xfs: xfs_readsb needs to check for magic numbers
  xfs: block allocation work needs to be kswapd aware
  xfs: remove redundant geometry information from xfs_da_state
  xfs: replace attr LBSIZE with xfs_da_geometry
  xfs: pass xfs_da_args to xfs_attr_leaf_newentsize
  xfs: use xfs_da_geometry for block size in attr code
  xfs: remove mp->m_dir_geo from directory logging
  xfs: reduce direct usage of mp->m_dir_geo
  xfs: move node entry counts to xfs_da_geometry
  xfs: convert dir/attr btree threshold to xfs_da_geometry
  xfs: convert m_dirblksize to xfs_da_geometry
  xfs: convert m_dirblkfsbs to xfs_da_geometry
  xfs: convert directory segment limits to xfs_da_geometry
  xfs: convert directory db conversion to xfs_da_geometry
  xfs: convert directory dablk conversion to xfs_da_geometry
  ...

The kernel has no concept of capabilities with respect to inodes; inodes
exist independently of namespaces.  For example, inode_capable(inode,
CAP_LINUX_IMMUTABLE) would be nonsense.

This patch changes inode_capable to check for uid and gid mappings and
renames it to capable_wrt_inode_uidgid, which should make it more
obvious what it does.

Fixes CVE-2014-4014.

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Serge Hallyn <serge.hallyn@ubuntu.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: stable@vger.kernel.org
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>