swap migration's isolate_lru_page() currently uses an IPI to notify other
processors that the lru caches need to be drained if the page cannot be
found on the LRU.  The IPI interrupt may interrupt a processor that is just
processing lru requests and cause a race condition.

This patch introduces a new function run_on_each_cpu() that uses the
keventd() to run the LRU draining on each processor.  Processors disable
preemption when dealing the LRU caches (these are per processor) and thus
executing LRU draining from another process is safe.

Thanks to Lee Schermerhorn <lee.schermerhorn@hp.com> for finding this race
condition.
Signed-off-by: NChristoph Lameter <clameter@sgi.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

Tracked this down on an Ultra Enterprise 3000.  It's a 6-way machine.  Odd
thing about this machine (and it's good for finding bugs like this) is that
the CPU id's are not 0 based.  For instance, on my machine the CPU's are
6/7/10/11/14/15.

This caused some NULL pointer dereference in kernel/workqueue.c because for
single_threaded workqueue's, it hardcoded the cpu to 0.

I changed the 0's to any_online_cpu(cpu_online_mask), which cpumask.h
claims is "First cpu in mask".  So this fits the same usage.
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

Replace smp_processor_id() with any_online_cpu(cpu_online_map) in order to
avoid lots of "BUG: using smp_processor_id() in preemptible [00000001]
code:..." messages in case taking a cpu online fails.

All the traces start at the last notifier_call_chain(...) in kernel/cpu.c.
Since we hold the cpu_control semaphore it shouldn't be any problem to access
cpu_online_map.

The reason why cpu_up failed is simply that the cpu that was supposed to be
taken online wasn't even there.  That is because on s390 we never know when a
new cpu comes and therefore cpu_possible_map consists of only ones and doesn't
reflect reality.
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

This patch makes the workqueus use alloc_percpu instead of an array.  The
workqueues are placed on nodes local to each processor.

The workqueue structure can grow to a significant size on a system with
lots of processors if this patch is not applied.  64 bit architectures with
all debugging features enabled and configured for 512 processors will not
be able to boot without this patch.
Signed-off-by: NChristoph Lameter <clameter@sgi.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

This patch introduces a kzalloc wrapper and converts kernel/ to use it.  It
saves a little program text.
Signed-off-by: NPekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: NAdrian Bunk <bunk@stusta.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

With "-W -Wno-unused -Wno-sign-compare" I get the following compile warning:

  CC      kernel/workqueue.o
kernel/workqueue.c: In function `workqueue_cpu_callback':
kernel/workqueue.c:504: warning: ordered comparison of pointer with integer zero

On error create_workqueue_thread() returns NULL, not negative pointer, so
following trivial patch suggests itself.
Signed-off-by: NMika Kukkonen <mikukkon@gmail.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

We have a chek in there to make sure that the name won't overflow
task_struct.comm[], but it's triggering for scsi with lots of HBAs, only
scsi is using single-threaded workqueues which don't append the "/%d"
anyway.

All too hard.  Just kill the BUG_ON.

Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@osdl.org>

[ kthread_create() uses vsnprintf() and limits the thing, so no
  actual overflow can actually happen regardless ]
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

This was unexported by Arjan because we have no current users.

However, during a conversion from tasklets to workqueues of the parisc led
functions, we ran across a case where this was needed.  In particular, the
open coded equivalent of cancel_rearming_delayed_workqueue was implemented
incorrectly, which is, I think, all the evidence necessary that this is a
useful API.
Signed-off-by: NJames Bottomley <James.Bottomley@SteelEye.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

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!