workqueue: gut flush[_delayed]_work_sync()

Now that all workqueues are non-reentrant, flush[_delayed]_work_sync()
are equivalent to flush[_delayed]_work().  Drop the separate
implementation and make them thin wrappers around
flush[_delayed]_work().

* start_flush_work() no longer takes @wait_executing as the only left
  user - flush_work() - always sets it to %true.

* __cancel_work_timer() uses flush_work() instead of wait_on_work().

Signed-off-by: Tejun Heo <tj@kernel.org>
workqueue: fix checkpatch issues

Fixed some checkpatch warnings.

tj: adapted to wq/for-3.7 and massaged pr_xxx() format strings a bit.

Signed-off-by: Valentin Ilie <valentin.ilie@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
LKML-Reference: <1345326762-21747-1-git-send-email-valentin.ilie@gmail.com>
workqueue: make all workqueues non-reentrant

By default, each per-cpu part of a bound workqueue operates separately
and a work item may be executing concurrently on different CPUs.  The
behavior avoids some cross-cpu traffic but leads to subtle weirdities
and not-so-subtle contortions in the API.

* There's no sane usefulness in allowing a single work item to be
  executed concurrently on multiple CPUs.  People just get the
  behavior unintentionally and get surprised after learning about it.
  Most either explicitly synchronize or use non-reentrant/ordered
  workqueue but this is error-prone.

* flush_work() can't wait for multiple instances of the same work item
  on different CPUs.  If a work item is executing on cpu0 and then
  queued on cpu1, flush_work() can only wait for the one on cpu1.

  Unfortunately, work items can easily cross CPU boundaries
  unintentionally when the queueing thread gets migrated.  This means
  that if multiple queuers compete, flush_work() can't even guarantee
  that the instance queued right before it is finished before
  returning.

* flush_work_sync() was added to work around some of the deficiencies
  of flush_work().  In addition to the usual flushing, it ensures that
  all currently executing instances are finished before returning.
  This operation is expensive as it has to walk all CPUs and at the
  same time fails to address competing queuer case.

  Incorrectly using flush_work() when flush_work_sync() is necessary
  is an easy error to make and can lead to bugs which are difficult to
  reproduce.

* Similar problems exist for flush_delayed_work[_sync]().

Other than the cross-cpu access concern, there's no benefit in
allowing parallel execution and it's plain silly to have this level of
contortion for workqueue which is widely used from core code to
extremely obscure drivers.

This patch makes all workqueues non-reentrant.  If a work item is
executing on a different CPU when queueing is requested, it is always
queued to that CPU.  This guarantees that any given work item can be
executing on one CPU at maximum and if a work item is queued and
executing, both are on the same CPU.

The only behavior change which may affect workqueue users negatively
is that non-reentrancy overrides the affinity specified by
queue_work_on().  On a reentrant workqueue, the affinity specified by
queue_work_on() is always followed.  Now, if the work item is
executing on one of the CPUs, the work item will be queued there
regardless of the requested affinity.  I've reviewed all workqueue
users which request explicit affinity, and, fortunately, none seems to
be crazy enough to exploit parallel execution of the same work item.

This adds an additional busy_hash lookup if the work item was
previously queued on a different CPU.  This shouldn't be noticeable
under any sane workload.  Work item queueing isn't a very
high-frequency operation and they don't jump across CPUs all the time.
In a micro benchmark to exaggerate this difference - measuring the
time it takes for two work items to repeatedly jump between two CPUs a
number (10M) of times with busy_hash table densely populated, the
difference was around 3%.

While the overhead is measureable, it is only visible in pathological
cases and the difference isn't huge.  This change brings much needed
sanity to workqueue and makes its behavior consistent with timer.  I
think this is the right tradeoff to make.

This enables significant simplification of workqueue API.
Simplification patches will follow.

Signed-off-by: Tejun Heo <tj@kernel.org>
workqueue: gut system_nrt[_freezable]_wq()

Now that all workqueues are non-reentrant, system[_freezable]_wq() are
equivalent to system_nrt[_freezable]_wq().  Replace the latter with
wrappers around system[_freezable]_wq().  The wrapping goes through
inline functions so that __deprecated can be added easily.

Signed-off-by: Tejun Heo <tj@kernel.org>
affs: stop setting bm_flags

AFFS stores values '1' and '2' in 'bm_flags', and I fail to see any logic when
it prefers one or another. AFFS writes '1' only from '->put_super()', while
'->sync_fs()' and '->write_super()' store value '2'.  So on the first glance,
it looks like we want to have '1' if we unmount.  However, this does not really
happen in these cases:
  1. superblock is written via 'write_super()' then we unmount;
  2. we re-mount R/O, then unmount.
which are quite typical.

I could not find good documentation describing this field, except of one random
piece of documentation in the internet which says that -1 means that the root
block is valid, which is not consistent with what we have in the Linux AFFS
driver.

Jan Kara commented on this: "I have some vague recollection that on Amiga
boolean was usually encoded as: 0 == false, ~0 == -1 == true. But it has been
ages..."

Thus, my conclusion is that value of '1' is as good as value of '2' and we can
just always use '2'. An Jan Kara suggested to go further: "generally bm_flags
handling looks strange. If they are 0, we mount fs read only and thus cannot
change them.  If they are != 0, we write 2 there. So IMHO if you just removed
bm_flags setting, nothing will really happen."

So this patch removes the bm_flags setting completely. This makes the "clean"
argument of the 'affs_commit_super()' function unneeded, so it is also removed.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
affs: remove useless superblock writeout on unmount

We do not need to write out the superblock from '->put_super()' because VFS has
already called '->sync_fs()' by this time and the superblock has already been
written out. Thus, remove the 'affs_commit_super()' infocation from
'affs_put_super()'.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
affs: remove useless superblock writeout on remount

We do not need to write out the superblock from '->remount_fs()' because
VFS has already called '->sync_fs()' by this time and the superblock has
already been written out. Thus, remove the 'affs_write_super()'
infocation from 'affs_remount()'.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
affs: re-structure superblock locking a bit

AFFS wants to serialize the superblock (the root block in AFFS terms) updates
and uses 'lock_super()/unlock_super()' for these purposes. This patch pushes the
locking down to the 'affs_commit_super()' from the callers.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
affs: stop using lock_super

The VFS's 'lock_super()' and 'unlock_super()' calls are deprecated and unwanted
and just wait for a brave knight who'd kill them. This patch makes AFFS stop
using them and use the buffer-head's own lock instead.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
affs: introduce VFS superblock object back-reference

Add an 'sb' VFS superblock back-reference to the 'struct affs_sb_info' data
structure - we will need to find the VFS superblock from a 'struct
affs_sb_info' object in the next patch, so this change is jut a preparation.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
affs: get rid of affs_sync_super

This patch makes affs stop using the VFS '->write_super()' method along with
the 's_dirt' superblock flag, because they are on their way out.

The whole "superblock write-out" VFS infrastructure is served by the
'sync_supers()' kernel thread, which wakes up every 5 (by default) seconds and
writes out all dirty superblocks using the '->write_super()' call-back.  But the
problem with this thread is that it wastes power by waking up the system every
5 seconds, even if there are no diry superblocks, or there are no client
file-systems which would need this (e.g., btrfs does not use
'->write_super()'). So we want to kill it completely and thus, we need to make
file-systems to stop using the '->write_super()' VFS service, and then remove
it together with the kernel thread.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
vfs: Rename end_writeback() to clear_inode()

After we moved inode_sync_wait() from end_writeback() it doesn't make sense
to call the function end_writeback() anymore. Rename it to clear_inode()
which well says what the function really does - set I_CLEAR flag.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
vfs: update documentation on ->i_dentry handling

we used to need to clean it in RCU callback freeing an inode;
in 3.2 that requirement went away.  Unfortunately, it hadn't
been reflected in Documentation/filesystems/porting.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
nfs: don't use intents for checking atomic open

is_atomic_open() is now only used by nfs4_lookup_revalidate() to check whether
it's okay to skip normal revalidation.

It does a racy check for mount read-onlyness and falls back to normal
revalidation if the open would fail.  This makes little sense now that this
function isn't used for determining whether to actually open the file or not.

The d_mountpoint() check still makes sense since it is an indication that we
might be following a mount and so open may not revalidate the dentry.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
CC: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
x86/mce: Fix siginfo_t->si_addr value for non-recoverable memory faults

In commit dad1743e5993f1 ("x86/mce: Only restart instruction after machine
check recovery if it is safe") we fixed mce_notify_process() to force a
signal to the current process if it was not restartable (RIPV bit not
set in MCG_STATUS). But doing it here means that the process doesn't
get told the virtual address of the fault via siginfo_t->si_addr. This
would prevent application level recovery from the fault.

Make a new MF_MUST_KILL flag bit for memory_failure() et al. to use so
that we will provide the right information with the signal.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Acked-by: Borislav Petkov <borislav.petkov@amd.com>
Cc: stable@kernel.org    # 3.4+
mm: have order > 0 compaction start off where it left

Order > 0 compaction stops when enough free pages of the correct page
order have been coalesced.  When doing subsequent higher order
allocations, it is possible for compaction to be invoked many times.

However, the compaction code always starts out looking for things to
compact at the start of the zone, and for free pages to compact things to
at the end of the zone.

This can cause quadratic behaviour, with isolate_freepages starting at the
end of the zone each time, even though previous invocations of the
compaction code already filled up all free memory on that end of the zone.

This can cause isolate_freepages to take enormous amounts of CPU with
certain workloads on larger memory systems.

The obvious solution is to have isolate_freepages remember where it left
off last time, and continue at that point the next time it gets invoked
for an order > 0 compaction.  This could cause compaction to fail if
cc->free_pfn and cc->migrate_pfn are close together initially, in that
case we restart from the end of the zone and try once more.

Forced full (order == -1) compactions are left alone.

[akpm@linux-foundation.org: checkpatch fixes]
[akpm@linux-foundation.org: s/laste/last/, use 80 cols]
Signed-off-by: Rik van Riel <riel@redhat.com>
Reported-by: Jim Schutt <jaschut@sandia.gov>
Tested-by: Jim Schutt <jaschut@sandia.gov>
Cc: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/compaction.c: fix deferring compaction mistake

Commit aff622495c9a ("vmscan: only defer compaction for failed order and
higher") fixed bad deferring policy but made mistake about checking
compact_order_failed in __compact_pgdat().  So it can't update
compact_order_failed with the new order.  This ends up preventing
correct operation of policy deferral.  This patch fixes it.

Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: have order > 0 compaction start near a pageblock with free pages

Commit 7db8889ab05b ("mm: have order > 0 compaction start off where it
left") introduced a caching mechanism to reduce the amount work the free
page scanner does in compaction.  However, it has a problem.  Consider
two process simultaneously scanning free pages

					    			C
	Process A		M     S     			F
			|---------------------------------------|
	Process B		M 	FS

	C is zone->compact_cached_free_pfn
	S is cc->start_pfree_pfn
	M is cc->migrate_pfn
	F is cc->free_pfn

In this diagram, Process A has just reached its migrate scanner, wrapped
around and updated compact_cached_free_pfn accordingly.

Simultaneously, Process B finishes isolating in a block and updates
compact_cached_free_pfn again to the location of its free scanner.

Process A moves to "end_of_zone - one_pageblock" and runs this check

                if (cc->order > 0 && (!cc->wrapped ||
                                      zone->compact_cached_free_pfn >
                                      cc->start_free_pfn))
                        pfn = min(pfn, zone->compact_cached_free_pfn);

compact_cached_free_pfn is above where it started so the free scanner
skips almost the entire space it should have scanned.  When there are
multiple processes compacting it can end in a situation where the entire
zone is not being scanned at all.  Further, it is possible for two
processes to ping-pong update to compact_cached_free_pfn which is just
random.

Overall, the end result wrecks allocation success rates.

There is not an obvious way around this problem without introducing new
locking and state so this patch takes a different approach.

First, it gets rid of the skip logic because it's not clear that it
matters if two free scanners happen to be in the same block but with
racing updates it's too easy for it to skip over blocks it should not.

Second, it updates compact_cached_free_pfn in a more limited set of
circumstances.

If a scanner has wrapped, it updates compact_cached_free_pfn to the end
	of the zone. When a wrapped scanner isolates a page, it updates
	compact_cached_free_pfn to point to the highest pageblock it
	can isolate pages from.

If a scanner has not wrapped when it has finished isolated pages it
	checks if compact_cached_free_pfn is pointing to the end of the
	zone. If so, the value is updated to point to the highest
	pageblock that pages were isolated from. This value will not
	be updated again until a free page scanner wraps and resets
	compact_cached_free_pfn.

This is not optimal and it can still race but the compact_cached_free_pfn
will be pointing to or very near a pageblock with free pages.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>