Messages in this thread | | | Date | Wed, 16 Oct 2013 10:43:22 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 4/6] Use raw_cpu_write for initialization of per cpu refcount. |
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On Tue, Oct 15, 2013 at 12:47:26PM -0500, Christoph Lameter wrote: > 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);
Just add: Safe to use raw because we're the only user. So we all instantly know.
> /* Backwards compatibility macros put refcount during init. */ > mod->waiter = current; > >
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