This is used by some MIPS systems

This deals with several things
- Codecs that think they are modems but are not
- Abstracting modem detection out of drivers
- Abstracting digital switching out of drivers
- Codecs that have no volume control
- Codec plugins for specific setups
- Codec plugins for things like touchscreen/batmon on AC97
- More codec handlers

The plugin API is intentionally modelled on the other driver_register
type interfaces.

#ra1

[Not tested as I no longer have the card]

fix cifs distributed caching - send oplock release immediately after flush of writebehind data on oplock break from server

into hostme.bitkeeper.com:/repos/c/cifs/linux-2.5cifs

We should only account file system requests, ones originating from
__make_request(). Otherwise it skews the counters and they go negative
really fast.

From: Davide Libenzi <davidel@xmailserver.org>

Fix epoll to allow pushing of multiple file descriptors sharing the same
kernel's file*

From: Andrey Borzenkov <arvidjaar@mail.ru>

I finally hit a painfully trivial way to reproduce another long standing devfs
problem - deadlock between devfs_lookup and devfs_d_revalidate_wait. When
devfs_lookup releases directory i_sem devfs_d_revalidate_wait grabs it (it
happens not for every path) and goes to wait to be waked up. Unfortunately,
devfs_lookup attempts to acquire directory i_sem before ever waking it up ...

To reproduce (2.5.74 UP or SMP - does not matter, single CPU system)

ls /dev/foo & rm -f /dev/foo &

or possibly in a loop but then it easily fills up process table. In my case it
hangs 100% reliably - on 2.5 OR 2.4.

The current fix is to move re-acquire of i_sem after all
devfs_d_revalidate_wait waiters have been waked up.  Much better fix would be
to ensure that ->d_revalidate either is always called under i_sem or always
without.  But that means the very heart of VFS and I do not dare to touch it.

The fix has been tested on 2.4 (and is part of unofficial Mandrake Club
kernel); I expected the same bug is in 2.5; I just was stupid not seeing the
way to reproduce it before.

From: Andrey Borzenkov <arvidjaar@mail.ru>

Doing concurrent lookups for the same name in devfs with devfsd and modules
enabled may result in stack coruption.

When devfs_lookup needs to call devfsd it arranges for other lookups for the
same name to wait. It is using local variable as wait queue head. After
devfsd returns devfs_lookup wakes up all waiters and returns. Unfortunately
there is no garantee all waiters will actually get chance to run and clean up
before devfs_lookup returns. so some of them attempt to access already freed
storage on stack.

It is trivial to trigger with SMP kernel (I have single-CPU system if it
matters) doing

while true
do
  ls /dev/foo &
done

Without spinlock debug system usually hung dead with reset button as the only
possibility.

I was not able to reproduce it on 2.4 on single-CPU system - in 2.4
devfs_d_revalidate_wait does not attempt to remove itself from wait queue
so it appears to be safe.

The patch makes lookup struct be allocated from heap and adds reference
counter to free it when no more needed.

From: Russell King <rmk@arm.linux.org.uk>

Interrupts can sometimes occur before the socket thread is started.

From: Daniel Ritz <daniel.ritz@gmx.ch>

init_socket() enables interrupts, and the interrupt handler does a wakeup.
Let's initialise that waitqueue head before turning on the interrupts.

From: William Lee Irwin III <wli@holomorphy.com>

There are reports of kernel threads being killed by the oomkiller.  We
think this is because the oom killer tries to kill a task after it has
exitted and set its ->mm to zero.  The oom killer will then try to kill all
other tasks which have a null ->mm.

Attempt to detect that case and fix it up.

From: Alex Tomas <bzzz@tmi.comex.ru>

fsync_super() calls ->sync_fs() just after ->write_super().  But
write_super() will start a commit.  In this case, ext3_sync_fs() will not
itself start a commit, and it hence forgets to wait on the commit which
ext3_write_super() started.

Fix that up by making journal_start_commit() return the transaction ID of
any currently-running transaction.

From: Alex Tomas <bzzz@tmi.comex.ru>

start_this_handle() takes into account t_outstanding_credits when calculating
log free space, but journal_next_log_block() accounts for blocks being logged
also.  Hence, blocks are accounting twice.  This effectively reduces the
amount of log space available to transactions and forces more commits.

Fix it by decrementing t_outstanding_credits each time we allocate a new
journal block.

From: Alex Tomas <bzzz@tmi.comex.ru>

Some transaction checkpointing improvements for the JBD commit phase.  Decent
speedups:

creation of 500K files in single dir (with htree, of course):
 before: 4m16.094s, 4m12.035s, 4m11.911s
 after:  1m41.364s, 1m43.461s, 1m45.189s

removal of 500K files in single dir:
 before: 43m50.161s
 after:  38m45.510s


- Make __log_wait_for_space() recalculate the needed blocks because journal
  free space changes during commit

- Make log_do_checkpoint() starts scanning from the oldest transaction

- Make log_do_checkpoint() stop scanning if a transaction gets dropped.
  The caller will reevaluate the transaction state and decide whether more
  space needs to be generated in the log.

  The effect of this is to smooth out the I/O patterns, avoid the huge
  stop-and-go which currently happens when forced checkpointing writes out
  and waits upon 3/4 of the journal's size worth of data.

From: Paul Clements <Paul.Clements@SteelEye.com>

Ensure that nbd and the block layer agree about device block sizes and total
device sizes.

From: Paul Clements <Paul.Clements@SteelEye.com>

Remove the unneeded nbd_open and nbd_release functions.

From: Paul Clements <Paul.Clements@SteelEye.com>

Modernise nbd.txt a bit.

From: Lou Langholtz <ldl@aros.net>

This fifth patch cleans up usage of the PARANOIA sanity checking macro and
code.  This patch modifies both drivers/block/nbd.c and
include/linux/nbd.h.  It's intended to be applied incrementally on top of
my fourth patch (4.1 really if you count the memset addition as .1's worth)
that simply removed unneeded blksize_bits field.  Again, I wanted to get
this smaller change out of the way before my next patch will is much more
major.

From: Lou Langholtz <ldl@aros.net>

Fixes the NBD oopses which people have been reporting.

From: Lou Langholtz <ldl@aros.net>

This fourth patch simply removes the blksize_bits field from the nbd_device
struct and driver implementation.  How this field made it into this driver
to begin with is a mystery (where was Al Viro when that patch was
submitted??).  :-)

This patch modifies both drivers/block/nbd.c and include/linux/nbd.h files.
 It's intended to be applied incrementally on top of my third patch (for
enhanced diagnostics support).

From: Lou Langholtz <ldl@aros.net>

This third patch (for enhancing diagnostics support) applies incrementally
after my last LKML'd patch (for cosmetic changes).  These changes introduce
configurable KERN_DEBUG level printk output for a variety of different
things that the driver does and provides the framework for enhanced future
debugging support as well.

From: Lou Langholtz <ldl@aros.net>

It's a helpful step in being better able to identify code inefficiencies
and problems particularly w.r.t.  locking.  It also modifies some of the
output messages for greater consistancy and better diagnostic support.

This second patch is a lead in that way to the third patch, which will
simply introduce the dprintk() debugging facility that my jumbo patch
originally had.

With the cosmetics patch and debugging enhancement (patch), it will make it
easier to fix or at least improve the locking bugs/races in NBD (that will
likely make up the fourth patch in my envisioned roadmap).

From: Ingo Molnar <mingo@elte.hu>

It makes hot-balancing happen in the 'busy tick' case as well, which should
spread out processes more agressively.

From: Maneesh Soni <maneesh@in.ibm.com>

While path walking we do follow_mount or follow_down which uses
dcache_lock for serialisation.  vfsmount related operations also use
dcache_lock for all updates. I think we can use a separate lock for
vfsmount related work and can improve path walking.

The following two patches does the same. The first one replaces
dcache_lock with new vfsmount_lock in namespace.c. The lock is
local to namespace.c and is not required outside. The second patch
uses RCU to have lock free lookup_mnt(). The patches are quite simple
and straight forward.

The lockmeter reults show reduced contention, and lock acquisitions
for dcache_lock while running dcachebench* on a 4-way SMP box

    SPINLOCKS         HOLD            WAIT
    UTIL  CON    MEAN(  MAX )   MEAN(  MAX )(% CPU)     TOTAL NOWAIT SPIN RJECT  NAME

  baselkm-2569:
    20.7% 20.9%  0.5us( 146us)  2.9us( 144us)(0.81%)  31590840 79.1% 20.9%    0%  dcache_lock
  mntlkm-2569:
    14.3% 13.6%  0.4us( 170us)  2.9us( 187us)(0.42%)  23071746 86.4% 13.6%    0%  dcache_lock

We get more than 8% improvement on 4-way SMP and 44% improvement on 16-way
NUMAQ while runing dcachebench*.

		Average (usecs/iteration)	Std. Deviation
		(lower is better)
4-way SMP
  2.5.69	15739.3				470.90
  2.5.69-mnt	14459.6				298.51

16-way NUMAQ
  2.5.69	120426.5			363.78
  2.5.69-mnt	 63225.8			427.60

*dcachebench is a microbenchmark written by Bill Hartner and is available at
http://www-124.ibm.com/developerworks/opensource/linuxperf/dcachebench/dcachebench.html

 vfsmount_lock.patch
 -------------------
 - Patch for replacing dcache_lock with new vfsmount_lock for all mount
   related operation. This removes the need to take dcache_lock while
   doing follow_mount or follow_down operations in path walking.

I re-ran dcachebench with 2.5.70 as base on 16-way NUMAQ box.

                	Average (usecs/iteration)       Std. Deviation
                	(lower is better)
16-way NUMAQ
2.5.70 				120710.9		 	230.67
 + vfsmount_lock.patch  	65209.6				242.97
    + lookup_mnt-rcu.patch 	64042.3				416.61

So just the lock splitting (vfsmount_lock.patch) gives almost similar benifits

From: "Chen, Kenneth W" <kenneth.w.chen@intel.com>

We hit a memory ordering race condition on AIO ring buffer tail pointer
between function aio_complete() and aio_read_evt().

What happens is that on an architecture that has a relaxed memory ordering
model like IPF(ia64), explicit memory barrier is required in a SMP
execution environment.  Considering the following case:

1 CPU is executing a tight loop of aio_read_evt.  It is pulling event off
the ring buffer.  During that loop, another CPU is executing aio_complete()
where it is putting event into the ring buffer and then update the tail
pointer.  However, due to relaxed memory ordering model, the tail pointer
can be visible before the actual event is being updated.  So the other CPU
sees the updated tail pointer but picks up a staled event data.

A memory barrier is required in this case between the event data and tail
pointer update.  Same is true for the head pointer but the window of the
race condition is nil.  For function correctness, it is fixed here as well.

By the way, this bug is fixed in the major distributor's kernel on 2.4.x
kernel series for a while, but somehow hasn't been propagated to 2.5 kernel
yet.