linux-stable.git/include/linux/cpumask.h, branch linux-2.6.24.y

CPU hotplug: fix cpu_is_offline() on !CONFIG_HOTPLUG_CPU

2008-01-06T20:39:42+00:00

make randconfig bootup testing found that the cpufreq code
crashes on bootup, if the powernow-k8 driver is enabled and
if maxcpus=1 passed on the boot line to a !CONFIG_HOTPLUG_CPU
kernel.

First lockdep found out that there's an inconsistent unlock
sequence:

 =====================================
 [ BUG: bad unlock balance detected! ]
 -------------------------------------
 swapper/1 is trying to release lock (&per_cpu(cpu_policy_rwsem, cpu)) at:
 [] unlock_policy_rwsem_write+0x3c/0x42
 but there are no more locks to release!

Call Trace:
 [] unlock_policy_rwsem_write+0x3c/0x42
 [] print_unlock_inbalance_bug+0x104/0x12c
 [] mark_held_locks+0x56/0x94
 [] unlock_policy_rwsem_write+0x3c/0x42
 [] cpufreq_add_dev+0x2a8/0x5c4
 ...

then shortly afterwards the cpufreq code crashed on an assert:

 ------------[ cut here ]------------
 kernel BUG at drivers/cpufreq/cpufreq.c:1068!
 invalid opcode: 0000 [1] SMP
 [...]
 Call Trace:
  [] sysdev_driver_unregister+0x5b/0x91
  [] cpufreq_register_driver+0x15d/0x1a2
  [] powernowk8_init+0x86/0x94
 [...]
 ---[ end trace 1e9219be2b4431de ]---

the bug was caused by maxcpus=1 bootup, which brought up the
secondary core as !cpu_online() but !cpu_is_offline() either,
which on on !CONFIG_HOTPLUG_CPU is always 0 (include/linux/cpu.h):

  /* CPUs don't go offline once they're online w/o CONFIG_HOTPLUG_CPU */
  static inline int cpu_is_offline(int cpu) { return 0; }

but the cpufreq code uses cpu_online() and cpu_is_offline() in
a mixed way - the low-level drivers use cpu_online(), while
the cpufreq core uses cpu_is_offline(). This opened up the
possibility to add the non-initialized sysdev device of the
secondary core:

 cpufreq-core: trying to register driver powernow-k8
 cpufreq-core: adding CPU 0
 powernow-k8: BIOS error - no PSB or ACPI _PSS objects
 cpufreq-core: initialization failed
 cpufreq-core: adding CPU 1
 cpufreq-core: initialization failed

which then blew up. The fix is to make cpu_is_offline() always
the negation of cpu_online(). With that fix applied the kernel
boots up fine without crashing:

 Calling initcall 0xffffffff80cc0510: powernowk8_init+0x0/0x94()
 powernow-k8: Found 1 AMD Athlon(tm) 64 X2 Dual Core Processor 3800+ processors (1 cpu cores) (version 2.20.00)
 powernow-k8: BIOS error - no PSB or ACPI _PSS objects
 initcall 0xffffffff80cc0510: powernowk8_init+0x0/0x94() returned -19.
 initcall 0xffffffff80cc0510 ran for 19 msecs: powernowk8_init+0x0/0x94()
 Calling initcall 0xffffffff80cc328f: init_lapic_nmi_sysfs+0x0/0x39()

We could fix this by making CPU enumeration aware of max_cpus, but that
would be more fragile IMO, and the cpu_online(cpu) != cpu_is_offline(cpu)
possibility was quite confusing and a continuous source of bugs too.

Most distributions have kernels with CPU hotplug enabled, so this bug
remained hidden for a long time.

Bug forensics:

The broken cpu_is_offline() API variant was introduced via:

 commit a59d2e4e6977e7b94e003c96a41f07e96cddc340
 Author: Rusty Russell 
 Date:   Mon Mar 8 06:06:03 2004 -0800

     [PATCH] minor cleanups for hotplug CPUs

( this predates linux-2.6.git, this commit is available from Thomas's
  historic git tree. )

Then 1.5 years later the cpufreq code made use of it:

 commit c32b6b8e524d2c337767d312814484d9289550cf
 Author: Ashok Raj 
 Date:   Sun Oct 30 14:59:54 2005 -0800

     [PATCH] create and destroy cpufreq sysfs entries based on cpu notifiers

 +       if (cpu_is_offline(cpu))
 +               return 0;

which is a correct use of the subtly broken new API. v2.6.15 then
shipped with this bug included.

then it took two more years for random-kernel qa to hit it.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Ingo Molnar 
Signed-off-by: Linus Torvalds

[PATCH] Convert highest_possible_processor_id to nr_cpu_ids

2007-02-21T01:10:13+00:00

We frequently need the maximum number of possible processors in order to
allocate arrays for all processors.  So far this was done using
highest_possible_processor_id().  However, we do need the number of
processors not the highest id.  Moreover the number was so far dynamically
calculated on each invokation.  The number of possible processors does not
change when the system is running.  We can therefore calculate that number
once.

Signed-off-by: Christoph Lameter 
Cc: Frederik Deweerdt 
Cc: Neil Brown 
Cc: Trond Myklebust 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] bitmap: parse input from kernel and user buffers

2006-10-11T18:14:22+00:00

lib/bitmap.c:bitmap_parse() is a library function that received as input a
user buffer.  This seemed to have originated from the way the write_proc
function of the /proc filesystem operates.

This has been reworked to not use kmalloc and eliminates a lot of
get_user() overhead by performing one access_ok before using __get_user().

We need to test if we are in kernel or user space (is_user) and access the
buffer differently.  We cannot use __get_user() to access kernel addresses
in all cases, for example in architectures with separate address space for
kernel and user.

This function will be useful for other uses as well; for example, taking
input for /sysfs instead of /proc, so it was changed to accept kernel
buffers.  We have this use for the Linux UWB project, as part as the
upcoming bandwidth allocator code.

Only a few routines used this function and they were changed too.

Signed-off-by: Reinette Chatre 
Signed-off-by: Inaky Perez-Gonzalez 
Cc: Paul Jackson 
Cc: Joe Korty 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] for_each_cpu_mask() warning fix

2006-06-25T17:01:12+00:00

On UP, this:

       cpumask_t mask = node_to_cpumask(numa_node_id());

       for_each_cpu_mask(cpu, mask)

does this:

mm/readahead.c: In function `node_readahead_aging':
mm/readahead.c:850: warning: unused variable `mask'

which is unpleasantly fixed by this:

Acked-by: Paul Jackson 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] remove for_each_cpu()

2006-06-25T17:00:54+00:00

Convert a few stragglers over to for_each_possible_cpu(), remove
for_each_cpu().

Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] for_each_possible_cpu: defines for_each_possible_cpu

2006-03-28T17:16:04+00:00

for_each_cpu() is a for-loop over cpu_possible_map.  for_each_online_cpu is
for-loop cpu over cpu_online_map.  .....for_each_cpu() is not sufficiently
explicit and can lead to mistakes.

This patch adds for_each_possible_cpu() in preparation for the removal of
for_each_cpu().

Signed-off-by: KAMEZAWA Hiroyuki 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] cpumask: uninline any_online_cpu()

2006-03-25T16:23:00+00:00

           text    data     bss     dec     hex filename
before: 3605597 1363528  363328 5332453  515de5 vmlinux
after:  3605295 1363612  363200 5332107  515c8b vmlinux

218 bytes saved.

Also, optimise any_online_cpu() out of existence on CONFIG_SMP=n.

This function seems inefficient.  Can't we simply AND the two masks, then use
find_first_bit()?

Cc: Paul Jackson 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] cpumask: uninline highest_possible_processor_id()

2006-03-25T16:23:00+00:00

Shrinks the only caller (net/bridge/netfilter/ebtables.c) by 174 bytes.

Also, optimise highest_possible_processor_id() out of existence on
CONFIG_SMP=n.

Cc: Paul Jackson 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] cpumask: uninline next_cpu()

2006-03-25T16:22:59+00:00

           text    data     bss     dec     hex filename
before: 3488027 1322496  360128 5170651  4ee5db vmlinux
after:  3485112 1322480  359968 5167560  4ed9c8 vmlinux

2931 bytes saved

Cc: Paul Jackson 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] cpumask: uninline first_cpu()

2006-03-25T16:22:59+00:00

           text    data     bss     dec     hex filename
before: 3490577 1322408  360000 5172985  4eeef9 vmlinux
after:  3488027 1322496  360128 5170651  4ee5db vmlinux

Cc: Paul Jackson 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds