Re: [PATCH] usb: musb: fix possible spinlock deadlock

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On Tue, Mar 28, 2017 at 07:15:58PM +0200, Greg KH wrote:
> On Tue, Mar 28, 2017 at 08:45:31AM -0500, Bin Liu wrote:
> > commit bc1e2154542071e3cfe1734b143af9b8bdacf8bd upstream.
> > 
> > The DSPS glue calls del_timer_sync() in its musb_platform_disable()
> > implementation, which requires the caller to not hold a lock. But
> > musb_remove() calls musb_platform_disable() will musb->lock held. This
> > could causes spinlock deadlock.
> > 
> > So change musb_remove() to call musb_platform_disable() without holds
> > musb->lock. This doesn't impact the musb_platform_disable implementation
> > in other glue drivers.
> > 
> > root@am335x-evm:~# modprobe -r musb-dsps
> > [  126.134879] musb-hdrc musb-hdrc.1: remove, state 1
> > [  126.140465] usb usb2: USB disconnect, device number 1
> > [  126.146178] usb 2-1: USB disconnect, device number 2
> > [  126.416985] musb-hdrc musb-hdrc.1: USB bus 2 deregistered
> > [  126.423943]
> > [  126.425525] ======================================================
> > [  126.431997] [ INFO: possible circular locking dependency detected ]
> > [  126.438564] 4.11.0-rc1-00003-g1557f13bca04-dirty #77 Not tainted
> > [  126.444852] -------------------------------------------------------
> > [  126.451414] modprobe/778 is trying to acquire lock:
> > [  126.456523]  (((&glue->timer))){+.-...}, at: [<c01b8788>] del_timer_sync+0x0/0xd0
> > [  126.464403]
> > [  126.464403] but task is already holding lock:
> > [  126.470511]  (&(&musb->lock)->rlock){-.-...}, at: [<bf30b7f8>] musb_remove+0x50/0x1
> > 30 [musb_hdrc]
> > [  126.479965]
> > [  126.479965] which lock already depends on the new lock.
> > [  126.479965]
> > [  126.488531]
> > [  126.488531] the existing dependency chain (in reverse order) is:
> > [  126.496368]
> > [  126.496368] -> #1 (&(&musb->lock)->rlock){-.-...}:
> > [  126.502968]        otg_timer+0x80/0xec [musb_dsps]
> > [  126.507990]        call_timer_fn+0xb4/0x390
> > [  126.512372]        expire_timers+0xf0/0x1fc
> > [  126.516754]        run_timer_softirq+0x80/0x178
> > [  126.521511]        __do_softirq+0xc4/0x554
> > [  126.525802]        irq_exit+0xe8/0x158
> > [  126.529735]        __handle_domain_irq+0x58/0xb8
> > [  126.534583]        __irq_usr+0x54/0x80
> > [  126.538507]
> > [  126.538507] -> #0 (((&glue->timer))){+.-...}:
> > [  126.544636]        del_timer_sync+0x40/0xd0
> > [  126.549066]        musb_remove+0x6c/0x130 [musb_hdrc]
> > [  126.554370]        platform_drv_remove+0x24/0x3c
> > [  126.559206]        device_release_driver_internal+0x14c/0x1e0
> > [  126.565225]        bus_remove_device+0xd8/0x108
> > [  126.569970]        device_del+0x1e4/0x308
> > [  126.574170]        platform_device_del+0x24/0x8c
> > [  126.579006]        platform_device_unregister+0xc/0x20
> > [  126.584394]        dsps_remove+0x14/0x30 [musb_dsps]
> > [  126.589595]        platform_drv_remove+0x24/0x3c
> > [  126.594432]        device_release_driver_internal+0x14c/0x1e0
> > [  126.600450]        driver_detach+0x38/0x6c
> > [  126.604740]        bus_remove_driver+0x4c/0xa0
> > [  126.609407]        SyS_delete_module+0x11c/0x1e4
> > [  126.614252]        __sys_trace_return+0x0/0x10
> > 
> > Fixes: ea2f35c01d5ea ("usb: musb: Fix sleeping function called from invalid context for hdrc glue")
> > Cc: <stable@xxxxxxxxxxxxxxx> #4.9+
> > Acked-by: Tony Lindgren <tony@xxxxxxxxxxx>
> > Signed-off-by: Bin Liu <b-liu@xxxxxx>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > 
> > Conflicts:
> > 	drivers/usb/musb/musb_core.c
> 
> What is this "Conflicts:" line for?

That was the reason the uptream commit failed to apply to stable
automatically.

I am not sure if we want to track it or not, so I leave it here for
comment.

Should I remove it?

Regards,
-Bin.
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