Starting with commit 57e73442 ("vsprintf: refactor %pK code out of
pointer"), the behavior of the raw '%p' printk format specifier was
changed to print a 32-bit hash of the pointer value to avoid leaking
kernel pointers into dmesg.  For most situations that's good.

This is /undesirable/ behavior when we're trying to debug XFS, however,
so define a PTR_FMT that prints the actual pointer when we're in debug
mode.

Note that %p for tracepoints still prints the raw pointer, so in the
long run we could consider rewriting some of these messages as
tracepoints.
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NDave Chinner <dchinner@redhat.com>

- Reports realtime device free blocks in statfs calls if (realtime)
  inheritance bit is set on the inode of directory, or realtime flag
  in the case of files.  This is a bit more intuitive, especially for
  use-cases which are using a much larger device for the realtime device.
- Add XFS_IS_REALTIME_MOUNT option to gate based on the existence of a
  realtime device on the mount, similar to the XFS_IS_REALTIME_INODE
  option.
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NRichard Wareing <rwareing@fb.com>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>

And move them to xfs_linux.h so that xfsprogs can stub them out more
easily.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>

Ever since we added the noinline tag there is no good reason to define
away the static for debug builds - we'll get just as good debug
information with our without it, so don't mess up sparse and other
checkers due to it.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>

Refactor the btree block header checks to have an internal function that
returns the address of the failing check without logging errors.  The
scrubber will call the internal function, while the external version
will maintain the current logging behavior.
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NDave Chinner <dchinner@redhat.com>

If using a kernel with CONFIG_XFS_RT=y and we set the RHINHERIT flag on
a directory in a filesystem that does not have a realtime device and
create a new file in that directory, it gets marked as a real time file.
When data is written and a fsync is issued, the filesystem attempts to
flush a non-existent rt device during the fsync process.

This results in a crash dereferencing a null buftarg pointer in
xfs_blkdev_issue_flush():

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
  IP: xfs_blkdev_issue_flush+0xd/0x20
  .....
  Call Trace:
    xfs_file_fsync+0x188/0x1c0
    vfs_fsync_range+0x3b/0xa0
    do_fsync+0x3d/0x70
    SyS_fsync+0x10/0x20
    do_syscall_64+0x4d/0xb0
    entry_SYSCALL64_slow_path+0x25/0x25

Setting RT inode flags does not require special privileges so any
unprivileged user can cause this oops to occur.  To reproduce, confirm
kernel is compiled with CONFIG_XFS_RT=y and run:

  # mkfs.xfs -f /dev/pmem0
  # mount /dev/pmem0 /mnt/test
  # mkdir /mnt/test/foo
  # xfs_io -c 'chattr +t' /mnt/test/foo
  # xfs_io -f -c 'pwrite 0 5m' -c fsync /mnt/test/foo/bar

Or just run xfstests with MKFS_OPTIONS="-d rtinherit=1" and wait.

Kernels built with CONFIG_XFS_RT=n are not exposed to this bug.

Fixes: f538d4da ("[XFS] write barrier support")
Cc: <stable@vger.kernel.org>
Signed-off-by: NRichard Wareing <rwareing@fb.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

XFS has a maximum symlink target length of 1024 bytes; this is a
holdover from the Irix days.  Unfortunately, the constant establishing
this is 'MAXPATHLEN' and is /not/ the same as the Linux MAXPATHLEN,
which is 4096.

The kernel enforces its 1024 byte MAXPATHLEN on symlink targets, but
xfsprogs picks up the (Linux) system 4096 byte MAXPATHLEN, which means
that xfs_repair doesn't complain about oversized symlinks.

Since this is an on-disk format constraint, put the define in the XFS
namespace and move everything over to use the new name.
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>

This is a purely mechanical patch that removes the private
__{u,}int{8,16,32,64}_t typedefs in favor of using the system
{u,}int{8,16,32,64}_t typedefs.  This is the sed script used to perform
the transformation and fix the resulting whitespace and indentation
errors:

s/typedef\t__uint8_t/typedef __uint8_t\t/g
s/typedef\t__uint/typedef __uint/g
s/typedef\t__int\([0-9]*\)_t/typedef int\1_t\t/g
s/__uint8_t\t/__uint8_t\t\t/g
s/__uint/uint/g
s/__int\([0-9]*\)_t\t/__int\1_t\t\t/g
s/__int/int/g
/^typedef.*int[0-9]*_t;$/d
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>

Use the common helper uuid_is_null() and remove the xfs specific
helper uuid_is_nil().

The common helper does not check for the NULL pointer value as
xfs helper did, but xfs code never calls the helper with a pointer
that can be NULL.

Conform comments and warning strings to use the term 'null uuid'
instead of 'nil uuid', because this is the terminology used by
lib/uuid.c and its users. It is also the terminology used in
userspace by libuuid and xfsprogs.
Signed-off-by: NAmir Goldstein <amir73il@gmail.com>
[hch: remove now unused uuid.[ch]]
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>

Our "little endian" UUID really is a Wintel GUID, so rename it and its
helpers such (guid_t).  The big endian UUID is the only true one, so
give it the name uuid_t.  The uuid_le and uuid_be names are retained for
now, but will hopefully go away soon.  The exception to that are the _cmp
helpers that will be replaced by better primitives ASAP and thus don't
get the new names.

Also the _to_bin helpers are named to match the better named uuid_parse
routine in userspace.

Also remove the existing typedef in XFS that's now been superceeded by
the generic type name.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
[andy: also update the UUID_LE/UUID_BE macros including fallout]
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: NAmir Goldstein <amir73il@gmail.com>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

Use the generic Linux definition to implement our UUID type, this will
allow using more generic infrastructure in the future.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NAmir Goldstein <amir73il@gmail.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>

Long ago, all this gunk was added with a lament about problems
with gcc's do_div, and a fun recommendation in the changelog:

 egcs-2.91.66 is the recommended compiler version for building XFS.

All this special stuff was needed to work around an old gcc bug,
apparently, and it's been there ever since.

There should be no need for this anymore, so remove it.

Remove the special 32-bit xfs_do_mod as well; just let the
kernel's do_div() handle all this.
Signed-off-by: NEric Sandeen <sandeen@redhat.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>

sched/headers: Prepare to move signal wakeup & sigpending methods from <linux/sched.h> into <linux/sched/signal.h>

Fix up affected files that include this signal functionality via sched.h.
Acked-by: NLinus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

The ASSERT() condition is the normal case, not the exception,
so testing the condition should be likely(), not unlikely().
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAmir Goldstein <amir73il@gmail.com>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>

This was entirely automated, using the script by Al:

  PATT='^[[:blank:]]*#[[:blank:]]*include[[:blank:]]*<asm/uaccess.h>'
  sed -i -e "s!$PATT!#include <linux/uaccess.h>!" \
        $(git grep -l "$PATT"|grep -v ^include/linux/uaccess.h)

to do the replacement at the end of the merge window.
Requested-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

On filesystems with a lot of metadata and in metadata intensive workloads
xfs_buf_find() is showing up at the top of the CPU cycles trace. Most of
the CPU time is spent on CPU cache misses while traversing the rbtree.

As the buffer cache does not need any kind of ordering, but fast lookups
a hashtable is the natural data structure to use. The rhashtable
infrastructure provides a self-scaling hashtable implementation and
allows lookups to proceed while the table is going through a resize
operation.

This reduces the CPU-time spent for the lookups to 1/3 even for small
filesystems with a relatively small number of cached buffers, with
possibly much larger gains on higher loaded filesystems.

[dchinner: reduce minimum hash size to an acceptable size for large
	   filesystems with many AGs with no active use.]
[dchinner: remove stale rbtree asserts.]
[dchinner: use xfs_buf_map for compare function argument.]
[dchinner: make functions static.]
[dchinner: remove redundant comments.]
Signed-off-by: NLucas Stach <dev@lynxeye.de>
Signed-off-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDave Chinner <david@fromorbit.com>

Trim CoW reservations made on behalf of a cowextsz hint if they get too
old or we run low on quota, so long as we don't have dirty data awaiting
writeback or directio operations in progress.

Garbage collection of the cowextsize extents are kept separate from
prealloc extent reaping because setting the CoW prealloc lifetime to a
(much) higher value than the regular prealloc extent lifetime has been
useful for combatting CoW fragmentation on VM hosts where the VMs
experience bursty write behaviors and we can keep the utilization ratios
low enough that we don't start to run out of space.  IOWs, it benefits
us to keep the CoW fork reservations around for as long as we can unless
we run out of blocks or hit inode reclaim.
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>

Instead we always declare struct xfs_dir2_sf_hdr as packed.  That's
the expected layout, and while most major architectures do the packing
by default the new structure size and offset checker showed that not
only the ARM old ABI got this wrong, but various minor embedded
architectures did as well.

[Verified that no code change on x86-64 results from this change]
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>

PAGE_CACHE_{SIZE,SHIFT,MASK,ALIGN} macros were introduced *long* time
ago with promise that one day it will be possible to implement page
cache with bigger chunks than PAGE_SIZE.

This promise never materialized.  And unlikely will.

We have many places where PAGE_CACHE_SIZE assumed to be equal to
PAGE_SIZE.  And it's constant source of confusion on whether
PAGE_CACHE_* or PAGE_* constant should be used in a particular case,
especially on the border between fs and mm.

Global switching to PAGE_CACHE_SIZE != PAGE_SIZE would cause to much
breakage to be doable.

Let's stop pretending that pages in page cache are special.  They are
not.

The changes are pretty straight-forward:

 - <foo> << (PAGE_CACHE_SHIFT - PAGE_SHIFT) -> <foo>;

 - <foo> >> (PAGE_CACHE_SHIFT - PAGE_SHIFT) -> <foo>;

 - PAGE_CACHE_{SIZE,SHIFT,MASK,ALIGN} -> PAGE_{SIZE,SHIFT,MASK,ALIGN};

 - page_cache_get() -> get_page();

 - page_cache_release() -> put_page();

This patch contains automated changes generated with coccinelle using
script below.  For some reason, coccinelle doesn't patch header files.
I've called spatch for them manually.

The only adjustment after coccinelle is revert of changes to
PAGE_CAHCE_ALIGN definition: we are going to drop it later.

There are few places in the code where coccinelle didn't reach.  I'll
fix them manually in a separate patch.  Comments and documentation also
will be addressed with the separate patch.

virtual patch

@@
expression E;
@@
- E << (PAGE_CACHE_SHIFT - PAGE_SHIFT)
+ E

@@
expression E;
@@
- E >> (PAGE_CACHE_SHIFT - PAGE_SHIFT)
+ E

@@
@@
- PAGE_CACHE_SHIFT
+ PAGE_SHIFT

@@
@@
- PAGE_CACHE_SIZE
+ PAGE_SIZE

@@
@@
- PAGE_CACHE_MASK
+ PAGE_MASK

@@
expression E;
@@
- PAGE_CACHE_ALIGN(E)
+ PAGE_ALIGN(E)

@@
expression E;
@@
- page_cache_get(E)
+ get_page(E)

@@
expression E;
@@
- page_cache_release(E)
+ put_page(E)
Signed-off-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This patch is the next step toward per-fs xfs stats. The patch makes
the show and clear routines able to handle any stats structure
associated with a kobject.

Instead of a single global xfsstats structure, add kobject and a pointer
to a per-cpu struct xfsstats. Modify the macros that manipulate the stats
accordingly: XFS_STATS_INC, XFS_STATS_DEC, and XFS_STATS_ADD now access
xfsstats->xs_stats.

The sysfs functions need to get from the kobject back to the xfsstats
structure which contains it, and pass the pointer to the ->xs_stats
percpu structure into the show & clear routines.
Signed-off-by: NBill O'Donnell <billodo@redhat.com>
Reviewed-by: NEric Sandeen <sandeen@redhat.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>

Just use char pointers directly instead of the confusing typedef to a
pointer type.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>

We can simply use a void pointer to pass a long return addresses in the
debugging helpers.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>

Replace uses of __psint_t with the proper uintptr_t and ptrdiff_t types,
and remove the defintions of __psint_t and __psunsigned_t.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>

Now that the in-core superblock infrastructure has been replaced with
generic per-cpu counters, we don't need it anymore. Nuke it from
orbit so we are sure that it won't haunt us again...
Signed-off-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>

More consolidatation for the on-disk format defintions.  Note that the
XFS_IS_REALTIME_INODE moves to xfs_linux.h instead as it is not related
to the on disk format, but depends on a CONFIG_ option.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>

The typedef for timespecs and nanotime() are completely unnecessary,
and delay() can be moved to fs/xfs/linux.h, which means this file
can go away.
Signed-off-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDave Chinner <david@fromorbit.com>

Move the IO flag definitions to xfs_inode.h and kill the header file
as it is now empty.

Removing the xfs_vnode.h file showed up an implicit header include
path:
	xfs_linux.h -> xfs_vnode.h -> xfs_fs.h

And so every xfs header file has been inplicitly been including
xfs_fs.h where it is needed or not. Hence the removal of xfs_vnode.h
causes all sorts of build issues because BBTOB() and friends are no
longer automatically included in the build. This also gets fixed.
Signed-off-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDave Chinner <david@fromorbit.com>

Trying to support tiny disks only and saving a bit memory might have
made sense on an SGI O2 15 years ago, but is pretty pointless today.

Remove the rarely tested codepath that uses various smaller in-memory
types to reduce our test matrix and make the codebase a little bit
smaller and less complicated.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NBen Myers <bpm@sgi.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>

Embed a base kobject into xfs_mount. This creates a kobject associated
with each XFS mount and a subdirectory in sysfs with the name of the
filesystem. The subdirectory lifecycle matches that of the mount. Also
add the new xfs_sysfs.[c,h] source files with some XFS sysfs
infrastructure to facilitate attribute creation.

Note that there are currently no attributes exported as part of the
xfs_mount kobject. It exists solely to serve as a per-mount container
for child objects.
Signed-off-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>

return is not a function.  "return(EIO);" is silly;
"return (EIO);" moreso.  return is not a function.
Nuke the pointless parens.

[dchinner: catch a couple of extra cases in xfs_attr_list.c,
xfs_acl.c and xfs_linux.h.]
Signed-off-by: NEric Sandeen <sandeen@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>

We want to distinguish between corruption, CRC errors,
etc.  In addition, the full stack trace on verifier errors
seems less than helpful; it looks more like an oops than
corruption.

Create a new function to specifically alert the user to
verifier errors, which can differentiate between
EFSCORRUPTED and CRC mismatches.  It doesn't dump stack
unless the xfs error level is turned up high.

Define a new error message (EFSBADCRC) to clearly identify
CRC errors.  (Defined to EBADMSG, bad message)
Signed-off-by: NEric Sandeen <sandeen@redhat.com>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>

Many/most callers of xfs_verify_cksum() pass bp->b_addr and
BBTOB(bp->b_length) as the first 2 args.  Add a helper
which can just accept the bp and the crc offset, and work
it out on its own, for brevity.
Signed-off-by: NEric Sandeen <sandeen@redhat.com>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>

Signed-off-by: NZhi Yong Wu <wuzhy@linux.vnet.ibm.com>
Reviewed-by: NMark Tinguely <tinguely@sgi.com>
Signed-off-by: NBen Myers <bpm@sgi.com>

Reviewed-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NGao feng <gaofeng@cn.fujitsu.com>
Signed-off-by: NDwight Engen <dwight.engen@oracle.com>
Signed-off-by: NBen Myers <bpm@sgi.com>

xfs_types.h is shared with userspace, so having kernel specific
types defined in it is problematic. Move all the kernel specific
defines to xfs_linux.h so we can remove the __KERNEL__ guards from
xfs_types.h.
Signed-off-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NMark Tinguely <tinguely@sgi.com>
Signed-off-by: NBen Myers <bpm@sgi.com>

Running a CONFIG_XFS_DEBUG kernel in production environments is not
the best idea as it introduces significant overhead, can change
the behaviour of algorithms (such as allocation) to improve test
coverage, and (most importantly) panic the machine on non-fatal
errors.

There are many cases where all we want to do is run a
kernel with more bounds checking enabled, such as is provided by the
ASSERT() statements throughout the code, but without all the
potential overhead and drawbacks.

This patch converts all the ASSERT statements to evaluate as
WARN_ON(1) statements and hence if they fail dump a warning and a
stack trace to the log. This has minimal overhead and does not
change any algorithms, and will allow us to find strange "out of
bounds" problems more easily on production machines.

There are a few places where assert statements contain debug only
code. These are converted to be debug-or-warn only code so that we
still get all the assert checks in the code.
Signed-off-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Signed-off-by: NBen Myers <bpm@sgi.com>

Ratelimited printk will be useful in printing xfs messages which are otherwise
not required to be printed always due to their high rate (to prevent kernel ring
buffer from overflowing), while at the same time required to be printed.
Signed-off-by: NRaghavendra D Prabhu <rprabhu@wnohang.net>
Reviewed-by: NRich Johnston <rjohnston@sgi.com>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NBen Myers <bpm@sgi.com>

 - add a mount feature bit for CRC enabled filesystems
 - add some helpers for generating and verifying the CRCs
 - add a copy_uuid helper

The checksumming helpers are loosely based on similar ones in sctp,
all other bits come from Dave Chinner.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NMark Tinguely <tinguely@sgi.com>
Signed-off-by: NBen Myers <bpm@sgi.com>

Create a new mount workqueue and delayed_work to enable background
scanning and freeing of eofblocks inodes. The scanner kicks in once
speculative preallocation occurs and stops requeueing itself when
no eofblocks inodes exist.

The scan interval is based on the new
'speculative_prealloc_lifetime' tunable (default to 5m). The
background scanner performs unfiltered, best effort scans (which
skips inodes under lock contention or with a dirty cache mapping).
Signed-off-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NMark Tinguely <tinguely@sgi.com>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NBen Myers <bpm@sgi.com>

Currently we have a few issues with the way the workqueue code is used to
implement AIL pushing:

 - it accidentally uses the same workqueue as the syncer action, and thus
   can be prevented from running if there are enough sync actions active
   in the system.
 - it doesn't use the HIGHPRI flag to queue at the head of the queue of
   work items

At this point I'm not confident enough in getting all the workqueue flags and
tweaks right to provide a perfectly reliable execution context for AIL
pushing, which is the most important piece in XFS to make forward progress
when the log fills.

Revert back to use a kthread per filesystem which fixes all the above issues
at the cost of having a task struct and stack around for each mounted
filesystem.  In addition this also gives us much better ways to diagnose
any issues involving hung AIL pushing and removes a small amount of code.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reported-by: NStefan Priebe <s.priebe@profihost.ag>
Tested-by: NStefan Priebe <s.priebe@profihost.ag>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NAlex Elder <aelder@sgi.com>