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Message-ID: <20131111082330.GA12405@gmail.com>
Date: Mon, 11 Nov 2013 09:23:30 +0100
From: Ingo Molnar <mingo@...nel.org>
To: wangbiao <biao.wang@...el.com>
Cc: oneukum@...e.de, netdev@...r.kernel.org, linux-usb@...r.kernel.org,
linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
mingo@...e.hu, a.p.zijlstra@...llo.nl, rusty@...tcorp.com.au,
william.douglas@...el.com
Subject: Re: [PATCH] usbnet: fix race condition caused spinlock bad magic
issue
* wangbiao <biao.wang@...el.com> wrote:
> @@ -1448,8 +1448,10 @@ static void usbnet_bh (unsigned long param)
>
> // waiting for all pending urbs to complete?
> if (dev->wait) {
> + wait_queue_head_t *wait_d = dev->wait;
> if ((dev->txq.qlen + dev->rxq.qlen + dev->done.qlen) == 0) {
> - wake_up (dev->wait);
> + if (wait_d)
> + wake_up(wait_d);
> }
>
> // or are we maybe short a few urbs?
1)
Nit: the scope of 'wait_d' is unnecessarily broad, it could be moved to
the block that uses it.
2)
Also, the changelog mentions that dev->wait can race - it would be nice to
add to the changelog what exact synchronization mechanism protects
usbnet_terminate_urbs() and usbnet_bh() from seeing/modifying that value
at once - as the code was clearly written without such interaction in
mind.
> @@ -1602,6 +1604,7 @@ usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
> init_timer (&dev->delay);
> mutex_init (&dev->phy_mutex);
> mutex_init(&dev->interrupt_mutex);
> + init_waitqueue_head(&unlink_wakeup);
3)
Can that runtime initialization be avoided by using
DECLARE_WAIT_QUEUE_HEAD()?
Thanks,
Ingo
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