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Subject[PATCH 4/6] Use raw_cpu_write for initialization of per cpu refcount.
The initialization of a structure is not subject to synchronization.
The use of __this_cpu would trigger a false positive with the
additional preemption checks for __this_cpu ops.

So simply disable the check through the use of raw_cpu ops.

Trace:

[ 0.668066] __this_cpu_write operation in preemptible [00000000] code: modprobe/286
[ 0.668108] caller is __this_cpu_preempt_check+0x38/0x60
[ 0.668111] CPU: 3 PID: 286 Comm: modprobe Tainted: GF 3.12.0-rc4+ #187
[ 0.668112] Hardware name: FUJITSU CELSIUS W530 Power/D3227-A1, BIOS V4.6.5.4 R1.10.0 for D3227-A1x 09/16/2013
[ 0.668113] 0000000000000003 ffff8807edda1d18 ffffffff816d5a57 ffff8807edda1fd8
[ 0.668117] ffff8807edda1d48 ffffffff8137359c ffff8807edda1ef8 ffffffffa0002178
[ 0.668121] ffffc90000067730 ffff8807edda1e48 ffff8807edda1d88 ffffffff813735f8
[ 0.668124] Call Trace:
[ 0.668129] [<ffffffff816d5a57>] dump_stack+0x4e/0x82
[ 0.668132] [<ffffffff8137359c>] check_preemption_disabled+0xec/0x110
[ 0.668135] [<ffffffff813735f8>] __this_cpu_preempt_check+0x38/0x60
[ 0.668139] [<ffffffff810c24fd>] load_module+0xcfd/0x2650
[ 0.668143] [<ffffffff816dd922>] ? page_fault+0x22/0x30
[ 0.668146] [<ffffffff810c3ef6>] SyS_init_module+0xa6/0xd0
[ 0.668150] [<ffffffff816e4fd3>] tracesys+0xe1/0xe6



Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Christoph Lameter <cl@linux.com>

Index: linux/kernel/module.c
===================================================================
--- linux.orig/kernel/module.c 2013-09-05 13:43:30.557687773 -0500
+++ linux/kernel/module.c 2013-10-07 12:33:43.732059759 -0500
@@ -643,7 +643,7 @@ static int module_unload_init(struct mod
INIT_LIST_HEAD(&mod->target_list);

/* Hold reference count during initialization. */
- __this_cpu_write(mod->refptr->incs, 1);
+ raw_cpu_write(mod->refptr->incs, 1);
/* Backwards compatibility macros put refcount during init. */
mod->waiter = current;



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