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From: Peter Rosin <>
To: Wolfram Sang <>, Wenwen Wang <>
Cc: Kangjie Lu <>,
	"open list:I2C SUBSYSTEM" <>,
	open list <>
Subject: Re: [PATCH v2 2/2] i2c: core-smbus: fix a potential missing-check bug
Date: Thu, 10 May 2018 15:36:21 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <20180510111658.sxf3mvye5q6ihxa7@ninjato>

On 2018-05-10 13:16, Wolfram Sang wrote:
> On Sat, May 05, 2018 at 08:02:21AM -0500, Wenwen Wang wrote:
>> In i2c_smbus_xfer_emulated(), the function i2c_transfer() is invoked to
>> transfer i2c messages. The number of actual transferred messages is
>> returned and saved to 'status'. If 'status' is negative, that means an
>> error occurred during the transfer process. In that case, the value of
>> 'status' is an error code to indicate the reason of the transfer failure.
>> In most cases, i2c_transfer() can transfer 'num' messages with no error.
>> And so 'status' == 'num'. However, due to unexpected errors, it is probable
>> that only partial messages are transferred by i2c_transfer(). As a result,
>> 'status' != 'num'. This special case is not checked after the invocation of
>> i2c_transfer() and can potentially lead to unexpected issues in the
>> following execution since it is expected that 'status' == 'num'.
>> This patch checks the return value of i2c_transfer() and returns an error
>> code -EIO if the number of actual transferred messages 'status' is not
>> equal to 'num'.
>> Signed-off-by: Wenwen Wang <>
> Applied to for-current, thanks!

I meant to comment here but got side-tracked and never got around to it.
But see e.g. [1] and [2] for drivers that will not be happy with this
change. Maybe there are more of those? I did a scan of the drivers in
algos/ and busses/, but there are drivers all over the tree that
implements .master_xfer that I have not audited. Who knows what further
problems this patch will reveal? So, maybe we should be a bit
conservative and only WARN as a first step?

Yes, I know that I suggested this, sorry for not following up with this
in a more timely fashion...



PS. Also busses/i2c-rcar.c seems like it might return a short "success"
for some sequence of events. But I'm not sure about that one...

  reply	other threads:[~2018-05-10 13:36 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-05 13:02 [PATCH v2 2/2] i2c: core-smbus: fix a potential missing-check bug Wenwen Wang
2018-05-10 11:16 ` Wolfram Sang
2018-05-10 13:36   ` Peter Rosin [this message]
2018-05-15  8:58     ` Wolfram Sang
2018-05-15 10:36       ` Peter Rosin
2018-05-17 13:06         ` Wolfram Sang
2018-05-17 13:38   ` Wolfram Sang

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