linux-kernel - Re: [RFC PATCH] pch_uart: Add eg20t_port lock field, avoid recursive spinlocks

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Message-ID: <20120619185432.30eb78c3@pyramind.ukuu.org.uk>
Date:	Tue, 19 Jun 2012 18:54:32 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Darren Hart <dvhart@...ux.intel.com>
Cc:	Tomoya MORINAGA <tomoya.rohm@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Feng Tang <feng.tang@...el.com>,
	Alexander Stein <alexander.stein@...tec-electronic.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alan Cox <alan@...ux.intel.com>, linux-serial@...r.kernel.org
Subject: Re: [RFC PATCH] pch_uart: Add eg20t_port lock field, avoid
 recursive spinlocks

> I see, the oops_in_progress test right? My thinking was that the
> oops_in_progress was only relevant to the port.lock as that could be
> taken outside of the pch_uart driver, while the priv.lock is only used
> within the driver. But, as the oops uses the pch_console_write itself, I
> can see the recursive spinlock failure case there.

Until your driver crashes...

> As for the printk, it seems the 8250 driver would also suffer from that
> in the serial8250_console_write function on the port.lock, and it does
> not make any allowances for printk.

I think 8250 probably wants fixing too then!

> 
> I would like to hold the priv.lock for a smaller window, but ordering
> requires that I take it prior to the port.lock.
> 
> So I can test for oops_in_progress on the priv->lock too, but that won't
> address the printk issue. Is the oops the bigger concern?

the oops is the main one - a printk would have to be in driver as a
screwup, and you can force an oops on a stall so pick it up later

Alan
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