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Subject[PATCH] stop_machine/cpu hotplug: fix disable_nonboot_cpus
From: Heiko Carstens <heiko.carstens@de.ibm.com>

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.

When introducing this new interface (9ea09af3bd3090e8349ca2899ca2011bd94cda85
"stop_machine: introduce stop_machine_create/destroy") I missed the second
call site of _cpu_down.
So add the missing stop_machine_create/destroy calls to disable_nonboot_cpus
as well.

Fixes suspend-to-ram/disk and also this bug:

[ 286.547348] BUG: unable to handle kernel paging request at 6b6b6b6b
[ 286.548940] IP: [<c0150ca4>] __stop_machine+0x88/0xe3
[ 286.550598] Oops: 0002 [#1] SMP
[ 286.560580] Pid: 3273, comm: halt Not tainted (2.6.28-06127-g238c6d5
[ 286.560580] EIP: is at __stop_machine+0x88/0xe3
[ 286.560580] Process halt (pid: 3273, ti=f1a28000 task=f4530f30
[ 286.560580] Call Trace:
[ 286.560580] [<c03d04e4>] ? _cpu_down+0x10f/0x234
[ 286.560580] [<c012a57e>] ? disable_nonboot_cpus+0x58/0xdc
[ 286.560580] [<c01360c0>] ? kernel_poweroff+0x22/0x39
[ 286.560580] [<c0136301>] ? sys_reboot+0xde/0x14c
[ 286.560580] [<c01331b2>] ? complete_signal+0x179/0x191
[ 286.560580] [<c0133396>] ? send_signal+0x1cc/0x1e1
[ 286.560580] [<c03de418>] ? _spin_unlock_irqrestore+0x2d/0x3c
[ 286.560580] [<c0133b65>] ? group_send_signal_info+0x58/0x61
[ 286.560580] [<c0133b9e>] ? kill_pid_info+0x30/0x3a
[ 286.560580] [<c0133d49>] ? sys_kill+0x75/0x13a
[ 286.560580] [<c01a06cb>] ? mntput_no_expire+ox1f/0x101
[ 286.560580] [<c019b3b3>] ? dput+0x1e/0x105
[ 286.560580] [<c018ef87>] ? __fput+0x150/0x158
[ 286.560580] [<c0157abf>] ? audit_syscall_entry+0x137/0x159
[ 286.560580] [<c010329f>] ? sysenter_do_call+0x12/0x34

Reported-by: "Justin P. Mattock" <justinmattock@gmail.com>
Reviewed-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
---
kernel/cpu.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

Index: linux-2.6/kernel/cpu.c
===================================================================
--- linux-2.6.orig/kernel/cpu.c
+++ linux-2.6/kernel/cpu.c
@@ -379,8 +379,11 @@ static cpumask_var_t frozen_cpus;

int disable_nonboot_cpus(void)
{
- int cpu, first_cpu, error = 0;
+ int cpu, first_cpu, error;

+ error = stop_machine_create();
+ if (error)
+ return error;
cpu_maps_update_begin();
first_cpu = cpumask_first(cpu_online_mask);
/* We take down all of the non-boot CPUs in one shot to avoid races
@@ -409,6 +412,7 @@ int disable_nonboot_cpus(void)
printk(KERN_ERR "Non-boot CPUs are not disabled\n");
}
cpu_maps_update_done();
+ stop_machine_destroy();
return error;
}


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