Re: [PATCH] stop_machine/cpu hotplug: fix disable_nonboot_cpus

[Ingo Molnar]

* Heiko Carstens <heiko.carstens@xxxxxxxxxx> wrote:

> From: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
> 
> disable_nonboot_cpus calls _cpu_down. But _cpu_down requires that the 
> caller already created the stop_machine workqueue (like cpu_down does). 
> Otherwise a call to stop_machine will lead to accesses to random memory 
> regions.

btw., i got this crash earlier today:

CPU0 attaching sched-domain:
 domain 0: span 0-1 level CPU
  groups: 0 1
CPU1 attaching sched-domain:
 domain 0: span 0-1 level CPU
  groups: 1 0
eth0: no IPv6 routers present
BUG: Bad page state in process cc1  pfn:00879
page:c101b894 flags:00000400 count:0 mapcount:0 mapping:(null) index:0
Pid: 3060, comm: cc1 Not tainted 2.6.28-tip-07641-gb97d41d-dirty #14985
Call Trace:
 [<c016ce8b>] bad_page+0xcf/0xe5
 [<c016d3b4>] free_pages_check+0xa7/0xc5
 [<c016d400>] free_hot_cold_page+0x2e/0x138
 [<c014751c>] ? __lock_acquire+0x127/0x29d
 [<c016d558>] free_hot_page+0xf/0x11
 [<c0170963>] put_page+0x76/0x7c
 [<c0185071>] ? constant_test_bit+0x9/0x20
 [<c0187149>] kfree+0x30/0xe5
 [<c0164993>] ? trace_hardirqs_on+0x8/0x1c
 [<c01547dd>] free_user_ns+0x1d/0x20
 [<c01547c0>] ? free_user_ns+0x0/0x20
 [<c02c7a41>] kref_put+0x18/0x22
 [<c0132d4c>] put_user_ns+0x16/0x18
 [<c0132f52>] free_uid+0x59/0xc8
 [<c0136239>] ? groups_free+0x36/0x3a
 [<c0140406>] put_cred_rcu+0x5f/0x70
 [<c01598fb>] __rcu_process_callbacks+0x168/0x1f8
 [<c03031be>] ? isicom_tx+0x0/0x31f
 [<c01599b1>] rcu_process_callbacks+0x26/0x46
 [<c012f11d>] __do_softirq+0x9d/0x139
 [<c012f080>] ? __do_softirq+0x0/0x139
 <IRQ>  [<c012efe2>] ? irq_exit+0x4c/0x83
 [<c05cc586>] ? __irqentry_text_start+0x6e/0x7c
 [<c0103f61>] ? apic_timer_interrupt+0x2d/0x34

and i applied your patch (from the other thread) and never saw this bug 
again.

So if it's the same bug (it appears to be) then you have my:

Tested-by: Ingo Molnar <mingo@xxxxxxx>


	Ingo
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