On Tue, Sep 03, 2024 at 05:29:02PM +0200, Gergo Koteles wrote:
> On Tue, 2024-09-03 at 18:14 +0300, Andy Shevchenko wrote:
> > On Tue, Sep 03, 2024 at 05:00:51PM +0200, Gergo Koteles wrote:
> > > On Thu, 2024-08-29 at 19:50 +0300, Andy Shevchenko wrote:
> > > > First of all, it's a bit counterintuitive to have something like
> > > >
> > > > int err;
> > > > ...
> > > > scoped_guard(...)
> > > > err = foo(...);
> > > > if (err)
> > > > return err;
> > > >
> > > > Second, with a particular kernel configuration and compiler version in
> > > > one of such cases the objtool is not happy:
> > > >
> > > > ideapad-laptop.o: warning: objtool: .text.fan_mode_show: unexpected end of section
> > > >
> > > > I'm not an expert on all this, but the theory is that compiler and
> > > > linker in this case can't understand that 'result' variable will be
> > > > always initialized as long as no error has been returned. Assigning
> > > > 'result' to a dummy value helps with this. Note, that fixing the
> > > > scoped_guard() scope (as per above) does not make issue gone.
> > > >
> > > > That said, assign dummy value and make the scope_guard() clear of its scope.
> > > > For the sake of consistency do it in the entire file.
> > > >
> > >
> > > Interestingly, if I open a scope manually and use the plain guard, the
> > > warning disappears.
> >
> > Yes, that's what I also have, but I avoid that approach because in that case
> > the printing will be done inside the lock, widening the critical section for
> > no benefits.
> >
>
> This is intended to be an inner block scope within the function, it
> does not expand the critical section.
I'm not sure I understand.
scoped_guard() has a marked scope (with {} or just a line coupled with it).
The guard() has a scope starting at it till the end of the function. In the
latter case the sysfs_emit() becomes part of the critical section.
> > > unsigned long result;
> > > int err;
> > >
> > > {
> > > guard(mutex)(&priv->vpc_mutex);
> > > err = read_ec_data(priv->adev->handle, VPCCMD_R_FAN,
> > > &result);
> > > if (err)
> > > return err;
> > > }
But looking again into the code above now I got what you meant.
You have added a nested scope inside the function, like
do {
...
} while (0);
Yes, this is strange and not what we want to have either. So I prefer to hear
what objtool / clang people may comment on this.
Sorry that I missed this.
> > > This looks a bit strange, but is probably easier for the compiler than
> > > the for loop of scoped_guard.
> > >
> > > But I don't know how well this style fits into the kernel.
--
With Best Regards,
Andy Shevchenko
