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Date: Mon, 18 Jan 2010 21:47:59 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Andreas Mohr <andi@lisas.de>
cc: linux-kernel@vger.kernel.org, Greg KH <greg@kroah.com>,
       Julia Lawall <julia@diku.dk>
Subject: Re: mcs7830 usb net: "scheduling while atomic" danger?
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On Mon, 18 Jan 2010, Andreas Mohr wrote:

> Hi,
> 
> drivers/net/usb/mcs7830.c does several:
> 
>         mutex_lock(&dev->phy_mutex);
>         /* write the MII command */
>         ret = mcs7830_set_reg(dev, HIF_REG_PHY_CMD1, 2, cmd);
>         if (ret < 0)
>                 goto out;
> 
>         /* wait for the data to become valid, should be within < 1ms */
>         for (i = 0; i < 10; i++) {
>                 ret = mcs7830_get_reg(dev, HIF_REG_PHY_CMD1, 2, cmd);
>                 if ((ret < 0) || (cmd[1] &
> HIF_REG_PHY_CMD2_READY_FLAG_BIT))
>                         break;
>                 ret = -EIO;
>                 msleep(1);
>         }
> 
> 
> Forgive me, but doesn't that mutex_lock()/msleep() (ab)use mean
> risking a "scheduling while atomic"?
> (such as discussed in e.g.
> http://search.luky.org/linux-kernel.2004/msg92817.html )

No, that's different. You are allowed to sleep with a mutex held. The
thread is about spin_lock()/msleep().

spin_lock() is implicitly disabling preemption, mutex_lock() does not.

Thanks,

	tglx