linux-kernel - Re: [PATCH] hwmon: pmbus: protect read-modify-write with lock

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Date:   Mon, 3 Jun 2019 09:18:02 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     "Sverdlin, Alexander (Nokia - DE/Ulm)" <alexander.sverdlin@...ia.com>
Cc:     "Adamski, Krzysztof (Nokia - PL/Wroclaw)" 
        <krzysztof.adamski@...ia.com>, Jean Delvare <jdelvare@...e.com>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] hwmon: pmbus: protect read-modify-write with lock

On Mon, Jun 03, 2019 at 01:11:45PM +0000, Sverdlin, Alexander (Nokia - DE/Ulm) wrote:
> Hi!
> 
> On 30/05/2019 08:45, Adamski, Krzysztof (Nokia - PL/Wroclaw) wrote:
> > The operation done in the pmbus_update_fan() function is a
> > read-modify-write operation but it lacks any kind of lock protection
> > which may cause problems if run more than once simultaneously. This
> > patch uses an existing update_lock mutex to fix this problem.
> > 
> > Signed-off-by: Krzysztof Adamski <krzysztof.adamski@...ia.com>
> > ---
> > 
> > I'm resending this patch to proper recipients this time. Sorry if the
> > previous submission confused anybody.
> > 
> >  drivers/hwmon/pmbus/pmbus_core.c | 11 ++++++++---
> >  1 file changed, 8 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> > index ef7ee90ee785..94adbede7912 100644
> > --- a/drivers/hwmon/pmbus/pmbus_core.c
> > +++ b/drivers/hwmon/pmbus/pmbus_core.c
> > @@ -268,6 +268,7 @@ int pmbus_update_fan(struct i2c_client *client, int page, int id,
> >  	int rv;
> >  	u8 to;
> >  
> > +	mutex_lock(&data->update_lock);
> >  	from = pmbus_read_byte_data(client, page,
> >  				    pmbus_fan_config_registers[id]);
> >  	if (from < 0)
> > @@ -278,11 +279,15 @@ int pmbus_update_fan(struct i2c_client *client, int page, int id,
> >  		rv = pmbus_write_byte_data(client, page,
> >  					   pmbus_fan_config_registers[id], to);
> >  		if (rv < 0)
> > -			return rv;
> > +			goto out;
> >  	}
> >  
> > -	return _pmbus_write_word_data(client, page,
> > -				      pmbus_fan_command_registers[id], command);
> > +	rv = _pmbus_write_word_data(client, page,
> > +				    pmbus_fan_command_registers[id], command);
> > +
> > +out:
> > +	mutex_lock(&data->update_lock);
> 
> This has to be mutex_unlock()...
> 

Not only that - it is also recursive.

Guenter