This patch allows the kernel to hold atomic kmaps in file_read_actor().

We try to fault in the page, then take an atomic kmap.  If the atomic
copy_to_user() then faults, drop a printk and fall back to kmap().

The patch implements the atomic copy_*_user() function.

If the kernel takes a pagefault while running copy_*_user() in an
atomic region, the copy_*_user() will fail (return a short value).

And with this patch, holding an atomic kmap() puts the CPU into an
atomic region.

- Increment preempt_count() in kmap_atomic() regardless of the
  setting of CONFIG_PREEMPT.  The pagefault handler recognises this as
  an atomic region and refuses to service the fault.  copy_*_user will
  return a non-zero value.

- Attempts to propagate the in_atomic() predicate to all the other
  highmem-capable architectures' pagefault handlers.  But the code is
  only tested on x86.

- Fixed a PPC bug in kunmap_atomic(): it forgot to reenable
  preemption if HIGHMEM_DEBUG is turned on.

- Fixed a sparc bug in kunmap_atomic(): it forgot to reenable
  preemption all the time, for non-fixmap pages.

- Fix an error in <linux/highmem.h> - in the CONFIG_HIGHMEM=n case,
  kunmap_atomic() takes an address, not a page *.

Fix a problem noticed by Ed Tomlinson: under shifting workloads the
shrink_zone() logic will refill the inactive load too slowly.

Bale out of the zone scan when we've reclaimed enough pages.  Fixes a
rarely-occurring problem wherein refill_inactive_zone() ends up
shuffling 100,000 pages and generally goes silly.

This needs to be revisited - we should go on and rebalance the lower
zones even if we reclaimed enough pages from highmem.

Back out the use of preempt_count to signify atomicity wrt pagefaults.
We won't do it that way - in_atomic() works fine.

Fix the ENOSPC recovery code in __block_write_full_page()

- Don't write out clean buffers.

- Set PG_writeback before submitting the IO.  Otherwise the completion
  handler will go BUG when it sees a non-PageWriteback page.  If the IO
  is very fast, or synchronous.

Patch from Bjorn Helgaas, via Rusty.

Change:

  On node 0 totalpages: 61031         <--- not including holes
  zone(0): 65172 pages.               <--- including holes
  zone(1): 0 pages.                   ...
  zone(2): 0 pages.

to:

  On node 0 totalpages: 61031         <--- not including holes
  DMA zone: 61031 pages               <--- not including holes
  Normal zone: 0 pages
  HighMem zone: 0 pages

Support POSIX compliant thread signals on a kernel level with usable
debugging (broadcast SIGSTOP, SIGCONT) and thread group management
(broadcast SIGKILL), plus to load-balance 'process' signals between
threads for better signal performance. 

Changes:

- POSIX thread semantics for signals

there are 7 'types' of actions a signal can take: specific, load-balance,
kill-all, kill-all+core, stop-all, continue-all and ignore. Depending on
the POSIX specifications each signal has one of the types defined for both
the 'handler defined' and the 'handler not defined (kernel default)' case.  
Here is the table:

 ----------------------------------------------------------
 |                    |  userspace       |  kernel        |
 ----------------------------------------------------------
 |  SIGHUP            |  load-balance    |  kill-all      |
 |  SIGINT            |  load-balance    |  kill-all      |
 |  SIGQUIT           |  load-balance    |  kill-all+core |
 |  SIGILL            |  specific        |  kill-all+core |
 |  SIGTRAP           |  specific        |  kill-all+core |
 |  SIGABRT/SIGIOT    |  specific        |  kill-all+core |
 |  SIGBUS            |  specific        |  kill-all+core |
 |  SIGFPE            |  specific        |  kill-all+core |
 |  SIGKILL           |  n/a             |  kill-all      |
 |  SIGUSR1           |  load-balance    |  kill-all      |
 |  SIGSEGV           |  specific        |  kill-all+core |
 |  SIGUSR2           |  load-balance    |  kill-all      |
 |  SIGPIPE           |  specific        |  kill-all      |
 |  SIGALRM           |  load-balance    |  kill-all      |
 |  SIGTERM           |  load-balance    |  kill-all      |
 |  SIGCHLD           |  load-balance    |  ignore        |
 |  SIGCONT           |  load-balance    |  continue-all  |
 |  SIGSTOP           |  n/a             |  stop-all      |
 |  SIGTSTP           |  load-balance    |  stop-all      |
 |  SIGTTIN           |  load-balancen   |  stop-all      |
 |  SIGTTOU           |  load-balancen   |  stop-all      |
 |  SIGURG            |  load-balance    |  ignore        |
 |  SIGXCPU           |  specific        |  kill-all+core |
 |  SIGXFSZ           |  specific        |  kill-all+core |
 |  SIGVTALRM         |  load-balance    |  kill-all      |
 |  SIGPROF           |  specific        |  kill-all      |
 |  SIGPOLL/SIGIO     |  load-balance    |  kill-all      |
 |  SIGSYS/SIGUNUSED  |  specific        |  kill-all+core |
 |  SIGSTKFLT         |  specific        |  kill-all      |
 |  SIGWINCH          |  load-balance    |  ignore        |
 |  SIGPWR            |  load-balance    |  kill-all      |
 |  SIGRTMIN-SIGRTMAX |  load-balance    |  kill-all      |
 ----------------------------------------------------------

as you can see it from the list, signals that have handlers defined never 
get broadcasted - they are either specific or load-balanced.

- CLONE_THREAD implies CLONE_SIGHAND

It does not make much sense to have a thread group that does not share
signal handlers. In fact in the patch i'm using the signal spinlock to
lock access to the thread group. I made the siglock IRQ-safe, thus we can
load-balance signals from interrupt contexts as well. (we cannot take the
tasklist lock in write mode from IRQ handlers.)

this is not as clean as i'd like it to be, but it's the best i could come
up with so far.

- thread group list management reworked.

threads are now removed from the group if the thread is unhashed from the
PID table. This makes the most sense. This also helps with another feature 
that relies on an intact thread group list: multithreaded coredumps.

- child reparenting reworked.

the O(N) algorithm in forget_original_parent() causes massive performance
problems if a large number of threads exit from the group. Performance 
improves more than 10-fold if the following simple rules are followed 
instead:

 - reparent children to the *previous* thread [exiting or not]
 - if a thread is detached then reparent to init.

- fast broadcasting of kernel-internal SIGSTOP, SIGCONT, SIGKILL, etc.

kernel-internal broadcasted signals are a potential DoS problem, since
they might generate massive amounts of GFP_ATOMIC allocations of siginfo
structures. The important thing to note is that the siginfo structure does
not actually have to be allocated and queued - the signal processing code
has all the information it needs, neither of these signals carries any
information in the siginfo structure. This makes a broadcast SIGKILL a
very simple operation: all threads get the bit 9 set in their pending
bitmask. The speedup due to this was significant - and the robustness win
is invaluable.

- sys_execve() should not kill off 'all other' threads.

the 'exec kills all threads if the master thread does the exec()' is a
POSIX(-ish) thing that should not be hardcoded in the kernel in this case.

to handle POSIX exec() semantics, glibc uses a special syscall, which
kills 'all but self' threads: sys_exit_allbutself().

the straightforward exec() implementation just calls sys_exit_allbutself()  
and then sys_execve().

(this syscall is also be used internally if the thread group leader
thread sys_exit()s or sys_exec()s, to ensure the integrity of the thread
group.)

Added PCI_BUS_NUM_RESOURCES as Ben suggested. Default value is 4
and can be overridden by arch (probably in asm/system.h).
pci_read_bridge_bases() and pci_assign_bus_resource() changed
accordingly. "for (i = 0 ; i < 4; i++)" in pci_add_new_bus() not
changed, as it's used _only_ for pci-pci and cardbus bridges.

This patch is based on changes I've used for 2.5.31, 2.5.31-mm1,
2.5.32-mm1, 2.5.32-mm2, and 2.5.33-mm1.

Without the patch, 2.5.x during heavy benchmark/stress testing
eventually locks up with these final messages:

kernel: qlogicfc0 : no handle slots, this should not happen.
kernel: hostdata->queued is 6, in_ptr: 7d

This is a combination of Doug Ledford's patch:
http://marc.theaimsgroup.com/?l=linux-kernel&m=103005703808312&w=2
and Eric Weigle's patch:
http://marc.theaimsgroup.com/?l=linux-kernel&m=103005790509079&w=2

2.5.33 (and all predecessors i've tested) locked up without it.

but it does...

into home.transmeta.com:/home/torvalds/v2.5/linux

	* we remove the paritition 0 from ->part[] and put the old
contents of ->part[0] into gendisk itself; indexes are shifted, obviously.
	* ->part is allocated at add_gendisk() time and freed at del_gendisk()
according to value of ->minor_shift; static arrays of hd_struct are gone
from drivers, ditto for manual allocations a-la ide.  As the matter of fact,
none of the drivers know about struct hd_struct now.

	new helpers - get_capacity(gendisk)/set_capacity(gendisk, sectors).
Drivers switched to these; that eliminates most of the accesses to
disk->part[]... in the drivers (and makes code more readable, while
we are at it).  That had caught several bugs when minor had been
used in place of minor>>minor_shift (acsi.c is especially nasty in
that respect; I don't know if it had ever been used with multiple
devices...)

	 ide switched from hwif->gd[i] to hwif->drive[i]->disk - IOW, instead
of array of two pointers to gendisks refered from hwif, we keep these pointers
in relevant drives.  Cleaned up.

	SCSI cdroms got gendisks.

	invalidate_buffers() pulled from cdrom ->reset() into its caller.
At that point only cdrom.c using cdi->dev.  That will play a bit later.

	minor cleanup in cdu31a.c

	mcdx.c cleaned up, uses of cdi->dev eliminated

	 pcd.c cleaned up, uses of cdi->dev eliminated, abuse of macros killed
(it used to have
#define PCD pcd[unit]
#define PI PCD.pi
and expected 'unit' to be local variable in each function that used these
(== almost every function in there)).

	Lindent pcd.c.

	 pcd.c - killed RR and WR macros (replaced with inlines without hidden
arguments; the first step in cleanup, they were monstrous).

	sbpcd.c - d eliminated, ditto for uses of cdi->dev (we set cdi->handle
pointing to structure we neeed).  Cleaned up a bit.

	 sbpcd.[c,h] - uses of D_S[d] replaced with uses of *current_drive.

	sbpcd.c - sigh... It used to have a global variable inventively called
'd'.  Current disk number.  Tons of uses, 99% of them being D_S[d].<blah>.
Added a new variable - current_drive.  Said animal is equal to D_S + d -
it's reassigned at the same place as d.

	 killed passing minors around; we always pass a pointer to structure;
scsi_CDs made static.  That killed uses of cdi->dev in sr.c and friends.

	Global search'n'replace job - 'SCp' (Scsi_CD pointer - I'm not kidding;
and yes, they spell it "Scsi") replaced with 'cd' (sr.c, sr_ioctl.c,
sr_vendor.c).

	sr.c: we set SCp->cdi.name from the very beginning, which allows
to kill passing minors in many cases (we can use "%s...", SCp->cd.name instead
of "sr%d...", minor and that turns out to be the majority of places where
we use minors at all).

	new helper - update_partition(disk, partition_number); does the
right thing wrt devfs and driverfs (un)registration of partition entries.
BLKPG ioctls fixed - now they call that beast rather than calling only
devfs side.  New helper - rescan_partitions(disk, bdev); does all work
with wiping/rereading/etc. and fs/block_dev.c now uses it instead of
check_partition().  The latter became static.

	similar to ->flags and ->driverfs_dev_arr, ->de_arr[] got replaced
with its (single) element + flag.

	Each hd_struct used to have int number; in it.  It's used _only_
in disk->part[0] - disk->part[n].number is never assigned/checked for any
positive n.  Moved from hd_struct to gendisk (disk->part[0].number to
disk->number).

	disk->driverfs_dev_arr is either NULL or consists of exactly one
element.  Same change as above (struct device ** -> struct device *); old
"is the pointer to array itself NULL or not?" replaced with a flag (in
disk->flags).

	Seeing that now disk->flags[] always consists of one element, we
replace char *flags with int flags, remove the junk from places that used
to allocate these "arrays" and do obvious updates of the code
(s/->flags[0]/->flags/).

	call of driverfs_remove_partitions() pulled into del_gendisk();
function isn't exported anymore.  Both it and driverfs_create_partitions()
cleaned up.

	driverfs_remove_partitions(), devfs_register_partitions(),
driverfs_create_partitions(), devfs_register_partition(), devfs_register_disc(),
had lost 'minor' argument - it's always disk->first_minor these days.
disk_name() takes partition number instead of minor now.  Callers of
wipe_partitions() in fs/block_dev.c expanded.  Remaining caller passes
gendisk instead of kdev_t now.

	Since ->nr_real is always 1 now, we can remove that field completely.
Removed the last remnants of switch in disk_name() (it could be killed
a long time ago, I just forgot to remove the last two cases when md and i2o
got converted).  Collapsed several instances of
disk->part[minor - disk->first_minor] - in cases when we know that we deal
with disk->part[0].

	wipe_partitions() and driverfs_register_partitions(..., 1) (i.e.
unregistering them) pulled into del_gendisk() and removed from callers.
grok_partitions() merged with register_disk().  devfs_register_partitions(),
grok_partitions() and wipe_partitions() not exported anymore.

Patch set from Jay Estabrook:

 - include/asm-alpha/dma.h:
	Add MAX_DMA_ADDR for SABLE and ALCOR

 - include/asm-alpha/floppy.h:
	enable the full CROSS_64KB macro for all platforms

 - include/asm-alpha/core_t2.h:
	fix HAE usage

 - arch/alpha/kernel/pci.c:
	fiddle with quirk_cypress

 - arch/alpha/kernel/traps.c:
	prevent opDEC_check() from multiple calls (EV4 SMP SABLEs)

 - arch/alpha/kernel/proto.h:
	make t2_pci_tbi() real

 - arch/alpha/kernel/time.c:
	shorten timeout delay

 - arch/alpha/kernel/sys_alcor.c:
	use ALCOR_MAX_DMA_ADDR because of the 1GB limit on ISA devices

 - arch/alpha/kernel/core_t2.c:
	add S/G support and allow direct-map to handle 2GB of memory

 - arch/alpha/kernel/core_tsunami.c:
	rework alignment requirements for ISA DMA, esp. for ACER platforms

 - arch/alpha/kernel/sys_sable.c:
	fix MAX_DMA_ADDR for the 1GB limitation

 - arch/alpha/kernel/pci_impl.h:
	add T2_DEFAULT_MEM_BASE to help avoid HAE use

 - arch/alpha/kernel/pci_iommu.c:
	fix ISA_DMA_MASK calculation, and force ISA alignment to 64KB

 - add another argument to do_fork();
 - assorted compile fixes.

Tested on CIA (sparse config space) and Irongate (dense config space);
other platforms should work as they are similar to these two.

Access config space directly on rx164.