linux-kernel - Re: [PATCH v3] USB:gadget: Fix a warning while loading g_mass

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Message-ID: <Pine.LNX.4.44L0.1406130935500.1059-100000@iolanthe.rowland.org>
Date:	Fri, 13 Jun 2014 09:39:52 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Yang,Wei" <Wei.Yang@...driver.com>
cc:	balbi@...com, <mina86@...a86.com>, <andrzej.p@...sung.com>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] USB:gadget: Fix a warning while loading g_mass_storage

On Fri, 13 Jun 2014, Yang,Wei wrote:

> On 06/09/2014 02:19 PM, Wei.Yang@...driver.com wrote:
> > From: Yang Wei <Wei.Yang@...driver.com>
> >
> > While loading g_mass_storage module, the following warning
> > is triggered.
> >
> > WARNING: at drivers/usb/gadget/composite.c:
> > usb_composite_setup_continue: Unexpected call
> > Modules linked in: fat vfat minix nls_cp437 nls_iso8859_1 g_mass_storage
> > [<800179cc>] (unwind_backtrace+0x0/0x104) from [<80619608>] (dump_stack+0x20/0x24)
> > [<80619608>] (dump_stack+0x20/0x24) from [<80025100>] (warn_slowpath_common+0x64/0x74)
> > [<80025100>] (warn_slowpath_common+0x64/0x74) from [<800251cc>] (warn_slowpath_fmt+0x40/0x48)
> > [<800251cc>] (warn_slowpath_fmt+0x40/0x48) from [<7f047774>] (usb_composite_setup_continue+0xb4/0xbc [g_mass_storage])
> > [<7f047774>] (usb_composite_setup_continue+0xb4/0xbc [g_mass_storage]) from [<7f047ad4>] (handle_exception+0x358/0x3e4 [g_mass_storage])
> > [<7f047ad4>] (handle_exception+0x358/0x3e4 [g_mass_storage]) from [<7f048080>] (fsg_main_thread+0x520/0x157c [g_mass_storage])
> > [<7f048080>] (fsg_main_thread+0x520/0x157c [g_mass_storage]) from [<8004bc90>] (kthread+0x98/0x9c)
> > [<8004bc90>] (kthread+0x98/0x9c) from [<8000faec>] (kernel_thread_exit+0x0/0x8)
> >
> > The root cause is that the existing code fails to take into
> > account the possibility that common->new_fsg can change while
> > do_set_interface() is running, because the spinlock isn't held
> > at this point.
> >
> > Signed-off-by: Yang Wei <Wei.Yang@...driver.com>
> > Signed-off-by: Alan Stern <stern@...land.harvard.edu>
> > ---
> >   drivers/usb/gadget/f_mass_storage.c |    6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > Hi Alan,
> >
> > Thanks for your review, there are a few changes in v3:
> >
> > 1) Fix a coding style issue.
> > 2) Refine the commit log
> >
> > Regards
> > Wei
> 
> Ping, Alan, What do you think of it?

You should not have added my "Signed-off-by:"; I did not give you 
permission to do that.

Michal's comment about common->new_fsg not being protected by the lock 
is a good one.  It would be better for the patch description to say:

	The value of common->new_fsg that gets tested after
	do_set_interface() returns needs to be the same as the value
	used by do_set_interface().

With that change, you may add

Acked-by: Alan Stern <stern@...land.harvard.edu>

Alan Stern

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