linux-kernel - Re: [PATCH] i2c: core-smbus: don't trace smbus

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Date:   Tue, 5 Feb 2019 13:13:57 +0100
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     John Sperbeck <jsperbeck@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: core-smbus: don't trace smbus_reply data on errors

On Thu, Jan 03, 2019 at 09:49:27PM -0500, Steven Rostedt wrote:
> On Thu,  3 Jan 2019 16:42:03 -0800
> John Sperbeck <jsperbeck@...gle.com> wrote:
> 
> > If an smbus transfer fails, there's no guarantee that the output
> > buffer was written.  So, avoid copying from the output buffer when
> > tracing after an error.  This was 'mostly harmless', but would trip
> > up kasan checking if left-over cruft in byte 0 is a large length,
> > causing us to read from unwritten memory.
> > 
> > Signed-off-by: John Sperbeck <jsperbeck@...gle.com>
> > ---
> >  drivers/i2c/i2c-core-smbus.c |  2 +-
> >  include/trace/events/smbus.h | 10 +++++-----
> >  2 files changed, 6 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/i2c/i2c-core-smbus.c b/drivers/i2c/i2c-core-smbus.c
> > index 9cd66cabb84f..132119112596 100644
> > --- a/drivers/i2c/i2c-core-smbus.c
> > +++ b/drivers/i2c/i2c-core-smbus.c
> > @@ -585,7 +585,7 @@ s32 __i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr,
> >  trace:
> >  	/* If enabled, the reply tracepoint is conditional on read_write. */
> >  	trace_smbus_reply(adapter, addr, flags, read_write,
> > -			  command, protocol, data);
> > +			  command, protocol, data, res);
> >  	trace_smbus_result(adapter, addr, flags, read_write,
> >  			   command, protocol, res);
> >  
> > diff --git a/include/trace/events/smbus.h b/include/trace/events/smbus.h
> > index d2fb6e1d3e10..b6376a7c7e74 100644
> > --- a/include/trace/events/smbus.h
> > +++ b/include/trace/events/smbus.h
> > @@ -138,8 +138,8 @@ TRACE_EVENT_CONDITION(smbus_reply,
> >  	TP_PROTO(const struct i2c_adapter *adap,
> >  		 u16 addr, unsigned short flags,
> >  		 char read_write, u8 command, int protocol,
> > -		 const union i2c_smbus_data *data),
> > -	TP_ARGS(adap, addr, flags, read_write, command, protocol, data),
> > +		 const union i2c_smbus_data *data, int res),
> > +	TP_ARGS(adap, addr, flags, read_write, command, protocol, data, res),
> >  	TP_CONDITION(read_write == I2C_SMBUS_READ),
> 
> Hmm, instead of tracing nothing, as this is already a "conditional
> trace event", why not add to that condition:
> 
> 	TP_CONDITION(res >= 0 && read_write == I2C_SMBUS_READ),
> 
> Unless you want to still trace some data on failure.

John, any comment to this?


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