Nouveau - Jun 2020 - [PATCH] drm/nouveau/clk/gm20b: Fix memory leak in gm20b_clk_new

Hi Ben,
> > When gk20a_clk_ctor() returns an error code, pointer "clk"
> > should be released. It's the same when gm20b_clk_new()
> > returns from elsewhere following this call.
> This shouldn't be necessary.  If a subdev constructor fails, and
> returns a pointer, the core will call the destructor to clean things
> up.
> 
I'm not familiar with the behavior of the caller of gm20b_clk_new(). 
If the subdev constructor fails, the core will check the pointer
(here is "pclk"), then it's ok and there is no bug (Do you mean 
this?). If the core executes error handling code only according to 
the error code, there may be a memory leak bug (the caller cannot 
know if -ENOMEM comes from the failure of kzalloc or gk20a_clk_ctor). 
If the core always calls the destructor as long as the constructor 
fails (even if the kzalloc fails), we may have a double free bug. 

Would you like to give a more detailed explanation about the behavior
of the core? 

Regards,
Dinghao

On Mon, 1 Jun 2020 at 13:27, <dinghao.liu at zju.edu.cn>
wrote:
>
>
> Hi Ben,
>
> > > When gk20a_clk_ctor() returns an error code, pointer
"clk"
> > > should be released. It's the same when gm20b_clk_new()
> > > returns from elsewhere following this call.
> > This shouldn't be necessary.  If a subdev constructor fails, and
> > returns a pointer, the core will call the destructor to clean things
> > up.
> >
>
> I'm not familiar with the behavior of the caller of gm20b_clk_new().
> If the subdev constructor fails, the core will check the pointer
> (here is "pclk"), then it's ok and there is no bug (Do you
mean
> this?). If the core executes error handling code only according to
> the error code, there may be a memory leak bug (the caller cannot
> know if -ENOMEM comes from the failure of kzalloc or gk20a_clk_ctor).
> If the core always calls the destructor as long as the constructor
> fails (even if the kzalloc fails), we may have a double free bug.
>
> Would you like to give a more detailed explanation about the behavior
> of the core?
If there's *any* error, it'll check the pointer, if it's non-NULL,
it'll call the destructor.  If kzalloc() fails, the pointer will be
NULL, there's no double-free bug.  *every* subdev is written this way
to avoid duplicating cleanup logic.

Ben.
>
> Regards,
> Dinghao

On Mon, 1 Jun 2020 at 13:37, Ben Skeggs <skeggsb at gmail.com>
wrote:
>
> On Mon, 1 Jun 2020 at 13:27, <dinghao.liu at zju.edu.cn> wrote:
> >
> >
> > Hi Ben,
> >
> > > > When gk20a_clk_ctor() returns an error code, pointer
"clk"
> > > > should be released. It's the same when gm20b_clk_new()
> > > > returns from elsewhere following this call.
> > > This shouldn't be necessary.  If a subdev constructor fails,
and
> > > returns a pointer, the core will call the destructor to clean
things
> > > up.
> > >
> >
> > I'm not familiar with the behavior of the caller of
gm20b_clk_new().
> > If the subdev constructor fails, the core will check the pointer
> > (here is "pclk"), then it's ok and there is no bug (Do
you mean
> > this?). If the core executes error handling code only according to
> > the error code, there may be a memory leak bug (the caller cannot
> > know if -ENOMEM comes from the failure of kzalloc or gk20a_clk_ctor).
> > If the core always calls the destructor as long as the constructor
> > fails (even if the kzalloc fails), we may have a double free bug.
> >
> > Would you like to give a more detailed explanation about the behavior
> > of the core?
> If there's *any* error, it'll check the pointer, if it's
non-NULL,
> it'll call the destructor.  If kzalloc() fails, the pointer will be
> NULL, there's no double-free bug.  *every* subdev is written this way
> to avoid duplicating cleanup logic.
Actually, gm20b_clk_new_speedo0() may have a bug here if kzalloc()
fails as it doesn't overwrite the previous pointer from
gm20b_clk_new().  That whole ctor() sequence is written a little
strangely.
>
> Ben.
> >
> > Regards,
> > Dinghao