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SubjectRE: [EXT] Re: [PATCH] iio: accell: mma8452: free iio trigger pointer when cleanup
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Hi, Jonathan

Best Regards!
Anson Huang

> -----Original Message-----
>
> On Mon, 8 Apr 2019 02:07:24 +0000
> Anson Huang <anson.huang@nxp.com> wrote:
>
> > Hi, Jonathan
> >
> > Best Regards!
> > Anson Huang
> >
> > > -----Original Message-----
> > > From: Jonathan Cameron [mailto:jic23@kernel.org]
> > > Sent: 2019年4月7日 18:40
> > > To: Anson Huang <anson.huang@nxp.com>
> > > Cc: knaack.h@gmx.de; lars@metafoo.de; pmeerw@pmeerw.net;
> Leonard
> > > Crestez <leonard.crestez@nxp.com>; gustavo@embeddedor.com;
> > > martink@posteo.de; rtresidd@electromag.com.au;
> > > linux-iio@vger.kernel.org; linux-kernel@vger.kernel.org;
> > > dl-linux-imx <linux-imx@nxp.com>
> > > Subject: [EXT] Re: [PATCH] iio: accell: mma8452: free iio trigger
> > > pointer when cleanup
> > >
> > > WARNING: This email was created outside of NXP. DO NOT CLICK links
> > > or attachments unless you recognize the sender and know the content is
> safe.
> > >
> > >
> > >
> > > On Thu, 4 Apr 2019 08:02:05 +0000
> > > Anson Huang <anson.huang@nxp.com> wrote:
> > >
> > > > When mma8452 is built as module, once it is insmod and rmmod,
> > > > below kernel dump will show out, the root cause is module being
> > > > put twice if iio trigger pointer is NOT NULL, this patch frees iio
> > > > trigger pointer after iio trigger is unregistered to avoid below
> > > > kernel
> > > > dump:
> > > >
> > > > ------------[ cut here ]------------
> > > > WARNING: CPU: 3 PID: 270 at kernel/module.c:1145
> > > module_put+0xd0/0x188
> > > > Modules linked in: mma8452(-)
> > > > CPU: 3 PID: 270 Comm: rmmod Not tainted
> > > > 5.1.0-rc3-next-20190403-00022-g5ede0c9-dirty #1596 Hardware name:
> > > > Freescale i.MX6 Quad/DualLite (Device Tree) [<c011272c>]
> > > > (unwind_backtrace) from [<c010d094>] (show_stack+0x10/0x14)
> > > > [<c010d094>] (show_stack) from [<c0bdc160>]
> > > > (dump_stack+0xd8/0x10c) [<c0bdc160>] (dump_stack) from
> > > > [<c01275d8>] (__warn+0xf8/0x124) [<c01275d8>] (__warn) from
> > > > [<c0127714>]
> > > (warn_slowpath_null+0x3c/0x48)
> > > > [<c0127714>] (warn_slowpath_null) from [<c01ca4d0>]
> > > > (module_put+0xd0/0x188) [<c01ca4d0>] (module_put) from
> > > > [<c08a5bb4>]
> > > > (iio_device_unregister_trigger_consumer+0x18/0x24)
> > > > [<c08a5bb4>] (iio_device_unregister_trigger_consumer) from
> > > > [<c08a0ab4>] (iio_dev_release+0x20/0) [<c08a0ab4>]
> > > > (iio_dev_release) from [<c065c0e8>] (device_release+0x24/0x8c)
> > > > [<c065c0e8>]
> > > > (device_release) from [<c0be1810>] (kobject_put+0x74/0xd4)
> > > > [<c0be1810>] (kobject_put) from [<c0664dc0>]
> > > > (release_nodes+0x16c/0x1f0) [<c0664dc0>] (release_nodes) from
> > > > [<c0661b80>] (device_release_driver_internal+0xec/0x1a0)
> > > > [<c0661b80>] (device_release_driver_internal) from [<c0661c90>]
> > > > (driver_detach+0x44/0x80) [<c0661c90>] (driver_detach) from
> > > > [<c066096c>] (bus_remove_driver+0x4c/0xa0) [<c066096c>]
> > > > (bus_remove_driver) from [<c01cc1a4>]
> > > > (sys_delete_module+0x130/0x1dc) [<c01cc1a4>] (sys_delete_module)
> > > > from [<c0101000>]
> > > (ret_fast_syscall+0x0/0x28) Exception stack(0xe8d87fa8 to
> > > 0xe8d87ff0)
> > > > 7fa0: 0001ffc0 38616d6d be87bbf0 00000880 00000000
> be87be98
> > > > 7fc0: 0001ffc0 38616d6d 00323534 00000081 000a9744 be87bf81
> > > > 000a9790
> > > > 00000000
> > > > 7fe0: be87bbe8 be87bbd8 0001fe18 b6e381a0 irq event stamp: 4017
> > > > hardirqs last enabled at (4035): [<c0188a0c>]
> > > > console_unlock+0x400/0x630 hardirqs last disabled at (4052):
> > > > [<c018868c>] console_unlock+0x80/0x630 softirqs last enabled at
> > > > (4050): [<c0102698>] __do_softirq+0x458/0x554 softirqs last
> > > > disabled at (4069): [<c012ed6c>] irq_exit+0x130/0x180 ---[ end
> > > > trace
> > > > a7ba8f1823b1e073 ]---
> > > >
> > > > Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
> > > Good fine, but the fix is not in the best place. The key thing is
> > > that any assignment inside a driver to iio_dev->trig should be done
> > > with iio_trigger_get.
> > >
> > > indio_dev->trig = iio_trigger_get(trig). The intent is to avoid
> > > this exact double free, but also handle it correctly if we are using devm_
> for all the handling.
> > >
> > > I just did a grep and there are quite a few drivers not doing this
> > > though so it's one we should be more careful about.
> > >
> > > Hmm. Anyone fancy doing an audit of existing drivers and checking
> > > which ones have this problem? Some seem to do exactly what you have
> > > here, but that isn't a the best pattern to encourage.
> > >
> > > For this one would you mind trying with the iio_trigger_get approach
> > > and if I'm not missing something, send a v2 fixing it that way?
> >
> > With below patch to use iio_trigger_get, looks like
> > try_release_module_ref() will return 1 and cause try_stop_module()
> > return fail and we will see " rmmod: can't unload 'mma8452': Resource
> > temporarily unavailable ",
> >
> > As the module ref count check is before
> > iio_device_unregister_trigger_consumer() is called which will do
> iio_trigger_put(), so looks like there is still something wrong with the module
> ref count?
> Hmm. Drivers that grab their own triggers are a bit of a pain. We need the
> infrastructure to try to prevent trigger drivers going away, but it can cause
> self references.
>
> For this particular driver the validation is only that the trigger is not used with
> a different device. You can use a different trigger with this device I believe?
>
> As such, we shouldn't really be setting this default at all. However, removing
> it now will break userspace that is assuming the default trigger is set.
> (setting a trigger should always be a userspace decision, rather than hard
> coded unless there is a clear one to one mapping - mind you we have this
> same problem if we have a fixed trigger, though in that case we have
> trig_readonly set so we can know it's happening and there is an easy fix).
>
> The right option, I think, is to remove the trigger manually before removing
> the driver. This is admittedly a bit ugly.
>
> echo '' > /sys/bus/iio/devices/iio:\devicesX/current_trigger.
>
> rmmod mma8452
>
> Can you confirm if that works as expected?

After removing the current_trigger, below Oops will occur when remove the mma8452 module. Any other idea?

i.mx8mm-evk# cat /sys/bus/iio/devices/iio\:device2/trigger/current_trigger
mma8451-dev2
i.mx8mm-evk# echo > /sys/bus/iio/devices/iio\:device2/trigger/current_trigger
i.mx8mm-evk# cat /sys/bus/iio/devices/iio\:device2/trigger/current_trigger
i.mx8mm-evk#
i.mx8mm-evk#
i.mx8mm-evk#
i.mx8mm-evk#
i.mx8mm-evk# rmmod mma8452
[ 93.004967] Internal error: Oops - undefined instruction: 0 [#1] SMP ARM
[ 93.011696] Modules linked in: mma8452
[ 93.015460] CPU: 1 PID: 272 Comm: rmmod Not tainted 5.1.0-rc4-next-20190415-00009-gef9b7e5-dirty #1756
[ 93.024771] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
[ 93.031316] PC is at sys_delete_module+0x1c0/0x1dc
[ 93.036112] LR is at 0x32
[ 93.038739] pc : [<c01cc3d8>] lr : [<00000032>] psr: a0070013
[ 93.045012] sp : e8b23f58 ip : bf0041d3 fp : 00000000
[ 93.050242] r10: 00000081 r9 : e8b22000 r8 : c01011c4
[ 93.055472] r7 : 00000081 r6 : be85cbf0 r5 : c1908908 r4 : bf0041c0
[ 93.062004] r3 : bf0043fc r2 : 00000000 r1 : ffffffff r0 : 00000000
[ 93.068538] Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
[ 93.075677] Control: 10c5387d Table: 3875004a DAC: 00000051
[ 93.081429] Process rmmod (pid: 272, stack limit = 0x(ptrval))
[ 93.087267] Stack: (0xe8b23f58 to 0xe8b24000)
[ 93.091630] 3f40: 38616d6d 00323534
[ 93.099816] 3f60: 00000001 c190eb04 00000017 b6ea74e0 e8b23fb0 10c5387d 000a9758 00000002
[ 93.108001] 3f80: be85c72c c011799c 00000001 c0101068 00cd0c80 38f6dac7 0001ffc0 38616d6d
[ 93.116186] 3fa0: 00323534 c0101000 0001ffc0 38616d6d be85cbf0 00000880 00000000 be85ce98
[ 93.124370] 3fc0: 0001ffc0 38616d6d 00323534 00000081 000a9744 be85cf81 000a9790 00000000
[ 93.132555] 3fe0: be85cbe8 be85cbd8 0001fe18 b6e551a0 60070010 be85cbf0 00000000 00000000
[ 93.140746] [<c01cc3d8>] (sys_delete_module) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
[ 93.149014] Exception stack(0xe8b23fa8 to 0xe8b23ff0)
[ 93.154073] 3fa0: 0001ffc0 38616d6d be85cbf0 00000880 00000000 be85ce98
[ 93.162258] 3fc0: 0001ffc0 38616d6d 00323534 00000081 000a9744 be85cf81 000a9790 00000000
[ 93.170440] 3fe0: be85cbe8 be85cbd8 0001fe18 b6e551a0
[ 93.175501] Code: 0affffd6 ee072fba e3e0400a eaffffb2 (e7f001f2)
[ 93.181604] ---[ end trace d1b72b60c2108067 ]---
Segmentation fault

Anson.

>
> Thanks,
>
> Jonathan
> >
> > +++ b/drivers/iio/accel/mma8452.c
> > @@ -1468,17 +1468,15 @@ static int mma8452_trigger_setup(struct
> iio_dev *indio_dev)
> > if (ret)
> > return ret;
> >
> > - indio_dev->trig = trig;
> > + indio_dev->trig = iio_trigger_get(trig);
> >
> > Thanks,
> > Anson.
> >
> > >
> > > Thanks
> > >
> > > Jonathan
> > >
> > >
> > > > ---
> > > > drivers/iio/accel/mma8452.c | 4 +++-
> > > > 1 file changed, 3 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/iio/accel/mma8452.c
> > > > b/drivers/iio/accel/mma8452.c index 3027811..6b18177 100644
> > > > --- a/drivers/iio/accel/mma8452.c
> > > > +++ b/drivers/iio/accel/mma8452.c
> > > > @@ -1475,8 +1475,10 @@ static int mma8452_trigger_setup(struct
> > > > iio_dev
> > > > *indio_dev)
> > > >
> > > > static void mma8452_trigger_cleanup(struct iio_dev *indio_dev) {
> > > > - if (indio_dev->trig)
> > > > + if (indio_dev->trig) {
> > > > iio_trigger_unregister(indio_dev->trig);
> > > > + indio_dev->trig = NULL;
> > > > + }
> > > > }
> > > >
> > > > static int mma8452_reset(struct i2c_client *client)
> >

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