Hi,
On Mon, Mar 29, 2021 at 10:02:20AM -0300, Jason Gunthorpe wrote:
> On Mon, Mar 29, 2021 at 09:07:18AM +0300, Dan Carpenter wrote:
> > After the device_register() succeeds, then the correct way to clean up
> > is to call device_unregister(). The unregister calls both device_del()
> > and device_put(). Since this code was only device_del() it results in
> > a memory leak.
> >
> > Fixes: dacb12877d92 ("thunderbolt: Add support for on-board retimers")
> > Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > ---
> > This is from a new static checker warning. Not tested. With new
> > warnings it's also possible that I have misunderstood something
> > fundamental so review carefully etc.
>
> It looks OK to me
I agree too.
> Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Thanks for the review!
> This also highlights the code has an ordering issue too, it calls
> device_register() then goes to do tb_retimer_nvm_add() however
> device_register() makes sysfs attributes visible before the rt->nvm is
> initialized and this:
>
> static ssize_t nvm_authenticate_store(struct device *dev,
> struct device_attribute *attr, const char *buf, size_t count)
> {
> if (!rt->nvm) {
>
> Isn't strong enough to close the potential racing. The nvm should be
> setup before device_register and all the above tests in the sysfs
> deleted so we can rely on the CPU barriers built into
> device_register() for correctness.
>
> [which is a general tip, be very suspicious if device_register() is
> being error unwound]
The nvm is a separate (physical Linux) device that gets added under this
one. It cannot be added before AFAICT.
The code you refer actually looks like this:
static ssize_t nvm_authenticate_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t count)
{
...
if (!mutex_trylock(&rt->tb->lock)) {
ret = restart_syscall();
goto exit_rpm;
}
if (!rt->nvm) {
ret = -EAGAIN;
goto exit_unlock;
}
Idea here is that if the NVMem (nvm) is not yet registered the attribute is
there but we return -EAGAIN to the userspace.
