Noticed by Tom 'spot' Callaway.

Even on uniprocessor we always reported the number of physical
cpus in the system via /proc/cpuinfo.  But when this got changed
to use num_possible_cpus() it always reads as "1" on uniprocessor.
This change was unintentional.

So scan the firmware device tree and count the number of cpu
nodes, and report that, as we always did.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Make some changes to the NEED_RESCHED and POLLING_NRFLAG to reduce
confusion, and make their semantics rigid.  Improves efficiency of
resched_task and some cpu_idle routines.

* In resched_task:
- TIF_NEED_RESCHED is only cleared with the task's runqueue lock held,
  and as we hold it during resched_task, then there is no need for an
  atomic test and set there. The only other time this should be set is
  when the task's quantum expires, in the timer interrupt - this is
  protected against because the rq lock is irq-safe.

- If TIF_NEED_RESCHED is set, then we don't need to do anything. It
  won't get unset until the task get's schedule()d off.

- If we are running on the same CPU as the task we resched, then set
  TIF_NEED_RESCHED and no further action is required.

- If we are running on another CPU, and TIF_POLLING_NRFLAG is *not* set
  after TIF_NEED_RESCHED has been set, then we need to send an IPI.

Using these rules, we are able to remove the test and set operation in
resched_task, and make clear the previously vague semantics of
POLLING_NRFLAG.

* In idle routines:
- Enter cpu_idle with preempt disabled. When the need_resched() condition
  becomes true, explicitly call schedule(). This makes things a bit clearer
  (IMO), but haven't updated all architectures yet.

- Many do a test and clear of TIF_NEED_RESCHED for some reason. According
  to the resched_task rules, this isn't needed (and actually breaks the
  assumption that TIF_NEED_RESCHED is only cleared with the runqueue lock
  held). So remove that. Generally one less locked memory op when switching
  to the idle thread.

- Many idle routines clear TIF_POLLING_NRFLAG, and only set it in the inner
  most polling idle loops. The above resched_task semantics allow it to be
  set until before the last time need_resched() is checked before going into
  a halt requiring interrupt wakeup.

  Many idle routines simply never enter such a halt, and so POLLING_NRFLAG
  can be always left set, completely eliminating resched IPIs when rescheduling
  the idle task.

  POLLING_NRFLAG width can be increased, to reduce the chance of resched IPIs.
Signed-off-by: NNick Piggin <npiggin@suse.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Con Kolivas <kernel@kolivas.org>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

Run idle threads with preempt disabled.

Also corrected a bugs in arm26's cpu_idle (make it actually call schedule()).
How did it ever work before?

Might fix the CPU hotplugging hang which Nigel Cunningham noted.

We think the bug hits if the idle thread is preempted after checking
need_resched() and before going to sleep, then the CPU offlined.

After calling stop_machine_run, the CPU eventually returns from preemption and
into the idle thread and goes to sleep.  The CPU will continue executing
previous idle and have no chance to call play_dead.

By disabling preemption until we are ready to explicitly schedule, this bug is
fixed and the idle threads generally become more robust.

From: alexs <ashepard@u.washington.edu>

  PPC build fix

From: Yoichi Yuasa <yuasa@hh.iij4u.or.jp>

  MIPS build fix
Signed-off-by: NNick Piggin <npiggin@suse.de>
Signed-off-by: NYoichi Yuasa <yuasa@hh.iij4u.or.jp>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

It isn't needed any longer, as noted by Hugh Dickins.

We still need the flush routines, due to the one remaining
call site in hugetlb_prefault_arch_hook().  That can be
eliminated at some later point, however.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

sparc64 is unique among architectures in taking the page_table_lock in
its context switch (well, cris does too, but erroneously, and it's not
yet SMP anyway).

This seems to be a private affair between switch_mm and activate_mm,
using page_table_lock as a per-mm lock, without any relation to its uses
elsewhere.  That's fine, but comment it as such; and unlock sooner in
switch_mm, more like in activate_mm (preemption is disabled here).

There is a block of "if (0)"ed code in smp_flush_tlb_pending which would
have liked to rely on the page_table_lock, in switch_mm and elsewhere;
but its comment explains how dup_mmap's flush_tlb_mm defeated it.  And
though that could have been changed at any time over the past few years,
now the chance vanishes as we push the page_table_lock downwards, and
perhaps split it per page table page.  Just delete that block of code.

Which leaves the mysterious spin_unlock_wait(&oldmm->page_table_lock)
in kernel/fork.c copy_mm.  Textual analysis (supported by Nick Piggin)
suggests that the comment was written by DaveM, and that it relates to
the defeated approach in the sparc64 smp_flush_tlb_pending.  Just delete
this block too.
Signed-off-by: NHugh Dickins <hugh@veritas.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Doing a "SUNW,stop-self" firmware call on the other cpus is not the
correct thing to do when dropping into the firmware for a halt,
reboot, or power-off.

For now, just do nothing to quiet the other cpus, as the system should
be quiescent enough.  Later we may decide to implement smp_send_stop()
like the other SMP platforms do.

Based upon a report from Christopher Zimmermann.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

At boot time, determine the D-cache, I-cache and E-cache size and
line-size.  Use them in cache flushes when appropriate.

This change was motivated by discovering that the D-cache on
UltraSparc-IIIi and later are 64K not 32K, and the flushes done by the
Cheetah error handlers were assuming a 32K size.

There are still some pieces of code that are hard coding things and
will need to be fixed up at some point.

While we're here, fix the D-cache and I-cache parity error handlers
to run with interrupts disabled, and when the trap occurs at trap
level > 1 log the event via a counter displayed in /proc/cpuinfo.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

It appears that a memory barrier soon after a mispredicted
branch, not just in the delay slot, can cause the hang
condition of this cpu errata.

So move them out-of-line, and explicitly put them into
a "branch always, predict taken" delay slot which should
fully kill this problem.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

These two bits were accesses non-atomically from assembler
code.  So, in order to eliminate any potential races resulting
from that, move these pieces of state into two bytes elsewhere
in struct thread_info.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

arch/sparc64/kernel/smp.c:48: error: parse error before "__attribute__"
arch/sparc64/kernel/smp.c:49: error: parse error before "__attribute__"
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Older UltraSPARC-III chips have a P-Cache bug that makes us disable it
by default at boot time.

However, this does hurt performance substantially, particularly with
memcpy(), and the bug is _incredibly_ obscure.  I have never seen it
triggered in practice, ever.

So provide a "-P" boot option that forces the P-Cache on.  It taints
the kernel, so if it does trigger and cause some data corruption or
OOPS, we will find out in the logs that this option was on when it
happened.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!