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Message-Id: <20131203233253.391372972@linux.com>
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Date: Tue, 03 Dec 2013 17:32:48 -0600
From: Christoph Lameter <cl@linux.com>
To: Tejun Heo <tj@kernel.org>
Cc: akpm@linuxfoundation.org, rostedt@goodmis.org,
        linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: [PATCH 16/41] modules: Use raw_cpu_write for initialization of per cpu refcount.
References: <20131203233232.928771708@linux.com>
Content-Disposition: inline; filename=preempt_module
Sender: linux-kernel-owner@vger.kernel.org
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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

Signed-off-by: Christoph Lameter <cl@linux.com>

Index: linux/kernel/module.c
===================================================================
--- linux.orig/kernel/module.c	2013-12-02 16:07:51.644582143 -0600
+++ linux/kernel/module.c	2013-12-02 16:07:51.634582418 -0600
@@ -640,7 +640,7 @@ 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);
 
 	return 0;
 }