On 7/15/08, Jean Delvare <[EMAIL PROTECTED]> wrote: > On Tue, 15 Jul 2008 10:14:06 -0600, Jonathan Corbet wrote: > > Hi, Jean, > > > > > I am looking at this patch of yours: > > > > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=3db633ee352bfe20d4a2b0c3c8a46ce31a6c7149 > > > > > > I believe that no locking is needed in i2cdev_open(). Do you have any > > > reason to think it does? If not, can I simply revert this patch? > > > > Before now, i2cdev_open() has always had the protection of the BKL. > > When I pushed that locking down into the individual open() functions, I > > really had to take a pretty conservative approach and assume that the > > BKL was needed unless that was really obviously not the case. In > > i2cdev_open(), for example, there's: > > > > i2c_dev = i2c_dev_get_by_minor(minor); > > > > and I really don't know what keeps *i2c_dev from going away during the > > rest of the call. I'm *not* saying there is a problem here; I just > > don't know. So the only thing I could really do is to push the BKL > > down and let the maintainers sort it out. > > > > ...all of which is my long-winded way of saying that, if you're > > convinced that i2cdev_open() is safe in the absence of the BKL, feel > > free to take it out. > > > Good point. i2c_dev is guaranteed to stay thanks to the call to > i2c_get_adapter(), however it happens _after_ the call to > i2c_dev_get_by_minor(), so without additional locking, this is racy. > That being said, I'm not sure how lock_kernel() is supposed to help. Is > the BKL held when i2cdev_detach_adapter() is called? If not, then I > suspect that the current code is already racy. > > I'll look into this, thanks for the hint.
Is i2c-dev vulnerable to the i2c device disappearing, for example rmmod it? Would combining i2c-dev into i2c core and integrating it with the core's lock protection make things easier to lock? You could make a compile time option to remove it for small systems. If it's in the core is attach/detach adapter still needed? I haven't looked at any of this in detail, but i2c-dev is only 6K of code. Half of the 6K might disappear if integrated into the core. What happens if user space and an in-kernel user both try using the device? I've never tried doing that. Should the presence of an in-kernel user make the user space device disappear? -- Jon Smirl [EMAIL PROTECTED] _______________________________________________ i2c mailing list i2c@lm-sensors.org http://lists.lm-sensors.org/mailman/listinfo/i2c
