linux-kernel - Re: [PATCH v2] usb: typec: fusb302: Fix debugfs mutex initialisation

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Date:   Tue, 19 Mar 2019 13:45:11 +0200
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Marc Zyngier <marc.zyngier@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Guenter Roeck <linux@...ck-us.net>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] usb: typec: fusb302: Fix debugfs mutex initialisation

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@....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

I think I need to add that to the MAINTAINERS file.


thanks,

-- 
heikki