From: Alan Stern <stern@rowland.harvard.edu>
To: Michal Nazarewicz <mina86@mina86.com>
Cc: Wei.Yang@windriver.com, <balbi@ti.com>, <andrzej.p@samsung.com>,
<linux-usb@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3] USB:gadget: Fix a warning while loading g_mass_storage
Date: Fri, 13 Jun 2014 09:43:00 -0400 (EDT) [thread overview]
Message-ID: <Pine.LNX.4.44L0.1406130939540.1059-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <xa1td2ednnxo.fsf@mina86.com>
On Fri, 13 Jun 2014, Michal Nazarewicz wrote:
> > 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.
>
> common->new_fsg is not protected by common->lock so this justification
> is not valid.
That's true. A better justification would be that the same value of
new_fsg should be used in do_set_interface() and in the test that
follows.
> > @@ -2421,6 +2422,7 @@ static void handle_exception(struct fsg_common *common)
> > }
> > common->state = FSG_STATE_IDLE;
> > }
> > + new_fsg = common->new_fsg;
>
> Also, because common->new_fsg is not protected by common->lock, doing
> this under a lock is kinda pointless.
Yes, but it doesn't hurt.
> > spin_unlock_irq(&common->lock);
> >
> > /* Carry out any extra actions required for the exception */
> > @@ -2460,8 +2462,8 @@ static void handle_exception(struct fsg_common *common)
> > break;
> >
> > case FSG_STATE_CONFIG_CHANGE:
> > - do_set_interface(common, common->new_fsg);
> > - if (common->new_fsg)
> > + do_set_interface(common, new_fsg);
> > + if (new_fsg)
> > usb_composite_setup_continue(common->cdev);
>
> As far as I can tell, it's safe to move the assignment to new_fsg here,
> e.g.:
>
> new_fsg = common->new_fsg;
> do_set_interface(common, new_fsg);
> if (new_fsg)
> usb_composite_setup_continue(common->cdev);
That would be equally correct. I don't see any strong reason for
preferring one over the other.
> > break;
>
> But perhaps new_fsg should be protected by the lock. I think valid fix
> (which I did not test in *any* way) will be this:
No, I think this change is both too big and unnecessary.
common->new_fsg does not need protection; in a sense it is "owned" by
the composite driver.
Alan Stern
next prev parent reply other threads:[~2014-06-13 13:43 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-03 9:37 [PATCH v1] USB:gadget: Fix a warning while loading g_mass_storage Wei.Yang
2014-06-03 14:48 ` Alan Stern
2014-06-04 1:20 ` Yang,Wei
2014-06-04 1:45 ` Peter Chen
2014-06-04 3:16 ` Yang,Wei
2014-06-04 4:41 ` Peter Chen
2014-06-04 13:56 ` Alan Stern
2014-06-04 18:48 ` Paul Zimmerman
2014-06-05 1:30 ` Peter Chen
2014-06-05 14:21 ` Alan Stern
2014-06-04 2:34 ` Yang,Wei
2014-06-04 12:06 ` Andrzej Pietrasiewicz
2014-06-04 15:26 ` Alan Stern
2014-06-05 10:00 ` Andrzej Pietrasiewicz
2014-06-05 18:10 ` Alan Stern
2014-06-04 4:32 ` [PATCH v2] " Wei.Yang
2014-06-05 18:08 ` Alan Stern
2014-06-09 6:02 ` Yang,Wei
2014-06-09 6:19 ` [PATCH v3] " Wei.Yang
2014-06-13 6:22 ` Yang,Wei
2014-06-13 13:39 ` Alan Stern
2014-06-14 13:10 ` Yang,Wei
2014-06-13 9:44 ` Michal Nazarewicz
2014-06-13 13:43 ` Alan Stern [this message]
2014-06-13 14:57 ` Michal Nazarewicz
2014-06-15 2:40 ` [PATCH] " Wei.Yang
2014-06-15 2:42 ` Yang,Wei
2014-06-17 5:59 ` Yang,Wei
2014-06-17 14:18 ` Alan Stern
2014-06-18 1:08 ` Yang,Wei
2014-06-18 11:44 ` Michal Nazarewicz
2014-06-18 14:22 ` Alan Stern
2014-06-19 1:48 ` Yang,Wei
2014-06-17 18:20 ` Michal Nazarewicz
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