linux-kernel - [PATCH 4/6] Use raw_cpu_write for initialization of per cpu refcount.

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Message-Id: <00000141a8a87077-a9a7e172-13c4-4c7c-9fc7-1f054ae0a5c7-000000@email.amazonses.com>
Date:	Fri, 11 Oct 2013 17:55:13 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>
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@...tcorp.com.au>
Signed-off-by: Christoph Lameter <cl@...ux.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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