From: Guenter Roeck <linux@roeck-us.net>
To: Wolfram Sang <wsa@the-dreams.de>
Cc: linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] eeprom: at24: Add support for large EEPROMs connected to SMBus adapters
Date: Wed, 25 Mar 2015 07:11:31 -0700 [thread overview]
Message-ID: <5512C213.7030705@roeck-us.net> (raw)
In-Reply-To: <20150319213937.GA899@katana>
On 03/19/2015 02:39 PM, Wolfram Sang wrote:
>
>> Turns out this is really easy to reproduce. One process reads
>> the eeprom over and over again, another runs i2cdump in a loop,
>> and voila ... lots of corruptions. Scary, especially considering
>> how wide-spread this kind of i2c access is in the kernel.
>
> A coccinelle script should at least be able to find vulnerable code
> paths, maybe even fix it. But not today for me... Thanks for testing and
> sharing the results!
>
Wolfram,
just to give you an update: I do have some code, but it is a bit messy,
and it doesn't work well for ds2482 (the chip behind it still hangs up
if I access it in parallel through i2c-dev). On top of that, it causes
pretty significant slow-downs when accessing other devices on the same
bus at the same time. Not surprising, I guess, since it expands the scope
of the bus lock significantly.
I thought about introducing a client lock, but that does not work because
of the way i2c-dev is written (creating its own 'shadow' client structure).
An address lock (ie a client lock based on <bus, address> instead of one
residing in the client structure) seems to be too expensive.
So right now I don't really know how to proceed, or if to proceed at all.
I'll think about it some more, but given how wide-spread the problem is
in the kernel, I might just leave it alone, and keep the at24 changes
out of tree.
Ultimately, the real problem is how i2c-dev accesses a client, not how
i2c client drivers (who assume they have exclusive access to a chip)
handle multi-command sequences. Forcing extensive locking on all drivers
because of i2c-dev just doesn't seem to be the right thing to do.
Guenter
next prev parent reply other threads:[~2015-03-25 14:11 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-04 16:23 [PATCH] eeprom: at24: Add support for large EEPROMs connected to SMBus adapters Guenter Roeck
2015-02-04 17:47 ` Wolfram Sang
2015-02-04 19:08 ` Guenter Roeck
2015-02-04 23:35 ` Wolfram Sang
2015-02-05 0:26 ` Guenter Roeck
2015-02-05 14:40 ` Wolfram Sang
2015-02-05 17:53 ` Guenter Roeck
2015-02-12 4:01 ` Guenter Roeck
2015-02-16 12:09 ` Wolfram Sang
2015-02-16 15:37 ` Guenter Roeck
2015-03-17 4:20 ` Guenter Roeck
2015-03-18 13:27 ` Wolfram Sang
2015-03-19 3:24 ` Guenter Roeck
2015-03-19 8:16 ` Wolfram Sang
2015-03-19 13:30 ` Guenter Roeck
2015-03-19 17:43 ` Guenter Roeck
2015-03-19 21:39 ` Wolfram Sang
2015-03-25 14:11 ` Guenter Roeck [this message]
2015-03-25 16:15 ` Wolfram Sang
2015-03-25 16:37 ` Guenter Roeck
2015-03-27 8:09 ` Wolfram Sang
2015-03-27 12:51 ` Guenter Roeck
2015-03-27 13:01 ` Wolfram Sang
2015-03-27 13:14 ` Guenter Roeck
2015-03-27 15:27 ` Wolfram Sang
2015-03-27 15:42 ` Guenter Roeck
2015-02-04 20:33 ` Guenter Roeck
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