linux-kernel - Re: [PATCH 4/4] firewire: fw-core: react on bus resets while the config ROM is being fetched

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Date:	Thu, 24 Jan 2008 11:11:38 -0500
From:	Jarod Wilson <jwilson@...hat.com>
To:	Stefan Richter <stefanr@...6.in-berlin.de>
CC:	linux1394-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org,
	Kristian Høgsberg <krh@...hat.com>,
	Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: [PATCH 4/4] firewire: fw-core: react on bus resets while the
 config ROM is being fetched

Stefan Richter wrote:
> read_rom() obtained a fresh new fw_device.generation for each read
> transaction.  Hence it was able to continue reading in the middle of the
> ROM even if a bus reset happened.  However the device may have modified
> the ROM during the reset.  We would end up with a corrupt fetched ROM
> image then.
> 
> Although all of this is quite unlikely, it is not impossible.
> Therefore we now restart reading the ROM if the bus generation changed.
> 
> Side note:  The barrier in read_rom(), inserted by patch "firewire:
> enforce access order between generation and node ID" is not necessary
> anymore because the sequence of calls
> 	fw_device_init() ->
> 		read_bus_info_block() ->
> 			read_rom()
> 			read_rom()
> 			read_rom()
> 			...
> will take care that generation is read before node_id, won't it?
> 
> Signed-off-by: Stefan Richter <stefanr@...6.in-berlin.de>

Based on a quick read through the code path, coupled with empirical evidence,
yes, it appears safe to remove the barrier in read_rom().

Signed-off-by: Jarod Wilson <jwilson@...hat.com>

-- 
Jarod Wilson
jwilson@...hat.com

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