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Date:   Wed, 20 Mar 2019 16:07:08 +0000
From:   Marc Zyngier <marc.zyngier@arm.com>
To:     Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Guenter Roeck <linux@roeck-us.net>,
        <linux-usb@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] usb: typec: fusb302: Fix debugfs mutex
 initialisation
Message-ID: <20190320160708.5f31ff10@why.wild-wind.fr.eu.org>
In-Reply-To: <20190319114511.GS7752@kuha.fi.intel.com>
References: <20190318174906.10429-1-marc.zyngier@arm.com>
        <20190319114511.GS7752@kuha.fi.intel.com>
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On Tue, 19 Mar 2019 13:45:11 +0200
Heikki Krogerus <heikki.krogerus@linux.intel.com> wrote:

Heikki,

> On Mon, Mar 18, 2019 at 05:49:06PM +0000, Marc Zyngier wrote:
> > Running a kernel with the fusb302 driver and lockdep enabled
> > leads to an unpleasant warning:
> > 
> > [    4.617477] INFO: trying to register non-static key.
> > [    4.617930] the code is fine but needs lockdep annotation.
> > [    4.618418] turning off the locking correctness validator.
> > [    4.618913] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.1.0-rc1-00007-g3542533f3fc9 #13
> > [    4.619620] Hardware name: rockchip evb_rk3399/evb_rk3399, BIOS 2019.04-rc3-00124-g2feec69fb1 03/15/2019
> > [    4.620454] Call trace:
> > [    4.620693]  dump_backtrace+0x0/0x138
> > [    4.621028]  show_stack+0x24/0x30
> > [    4.621336]  dump_stack+0xbc/0x104
> > [    4.621649]  register_lock_class+0x594/0x598
> > [    4.622036]  __lock_acquire+0x80/0x11b8
> > [    4.622384]  lock_acquire+0xdc/0x260
> > [    4.622711]  __mutex_lock+0x90/0x8a0
> > [    4.623037]  mutex_lock_nested+0x3c/0x50
> > [    4.623394]  _fusb302_log+0x88/0x1f0
> > [    4.623721]  fusb302_log+0x7c/0xa0
> > [    4.624033]  tcpm_init+0x5c/0x190
> > [    4.624336]  tcpm_init+0x3c/0x130
> > [    4.624640]  tcpm_register_port+0x574/0x878
> > [    4.625019]  fusb302_probe+0x2c8/0x590
> > 
> > Despite what the message says, the code isn't fine, as it tries to
> > make use of the fusb302_log facility pretty early. This requires the
> > logbuffer_lock mutex to be initialised, but that only happens much
> > later. Boo.
> > 
> > Hoist the fusb302_debugfs_init call before tcpm_register_port so that
> > we can enjoy a working mutex. At Guenter's request, also add teardown
> > of the debugfs facility on the error path.
> > 
> > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>  
> 
> After applying this there was no more "fusb302" debugfs directory, and
> attempt to unload the fusb302 module dead locked. Also, attempt to
> reboot caused this to happen on my GDPWin board after applying the
> patch:
> 
>         BUG: Dentry 0000000012f2a05d{i=149,n=i2c-fusb302}  still in use (1) [unmount of sysfs sysfs]
>         WARNING: CPU: 3 PID: 1639 at fs/dcache.c:1529 umount_check.cold.55+0x2e/0x3a
>         Modules linked in: intel_xhci_usb_role_switch roles pi3usb30532 typec i915 intel_gtt intel_cht_int33fe [last unloaded: tcpm]
>         CPU: 3 PID: 1639 Comm: umount Not tainted 5.1.0-rc1-heikki+ #916
>         Hardware name: Default string Default string/Default string, BIOS 5.11 05/25/2017
>         RIP: 0010:umount_check.cold.55+0x2e/0x3a
>         ...
> 
> Note. Your patch has also a conflict with patches from Hans, I
> think with this one: https://patchwork.kernel.org/patch/10847275/
> I can take care of that, but you can also rebase the next version on
> top of my typec-next branch to solve that problem:
> https://github.com/krohei/linux/commits/typec-next

OK, this is very weird. I can't reproduce any of the issues you're
reporting:

- the patch applies cleanly on top of typec-next
- removing the fusb302 module works
- I see the debugfs file whenever fsusb302 is inserted

Maybe you were trying this on another branch?

Thanks,

	M.
-- 
Without deviation from the norm, progress is not possible.