Re: [PATCH] sysrq: Auto release device node using __free attribute

[Roman Storozhenko]

This change allows us to put this pointer under automatic scope
management and get rid of node_put.  Besides, if a new code path is
introduced we won't need to add a new of_node_put.

Thanks,
Roman

On Thu, Apr 11, 2024 at 8:11 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Thu, Apr 11, 2024 at 08:02:56PM +0200, Roman Storozhenko wrote:
> > Add a cleanup function attribute '__free(device_node)' to the device node
> > pointer initialization statement and remove the pairing cleanup function
> > call of 'of_node_put' at the end of the function.
> > The '_free()' attrubute is introduced by scope-based resource management
> > in-kernel framework implemented in 'cleanup.h'. A pointer marked with
> > '__free()' attribute makes a compiler insert a cleanup function call
> > to the places where the pointer goes out of the scope. This feature
> > allows to get rid of manual cleanup function calls.
> >
> > Suggested-by: Julia.Lawall <Julia.Lawall@xxxxxxxx>
> > Signed-off-by: Roman Storozhenko <romeusmeister@xxxxxxxxx>
> > ---
> > This patch targets the next tree:
> > tree: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
> > tag: next-20240411
> > ---
> >  drivers/tty/sysrq.c | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
> > index 02217e3c916b..1d1261f618c0 100644
> > --- a/drivers/tty/sysrq.c
> > +++ b/drivers/tty/sysrq.c
> > @@ -758,11 +758,12 @@ static void sysrq_detect_reset_sequence(struct sysrq_state *state,
> >  static void sysrq_of_get_keyreset_config(void)
> >  {
> >       u32 key;
> > -     struct device_node *np;
> >       struct property *prop;
> >       const __be32 *p;
> >
> > -     np = of_find_node_by_path("/chosen/linux,sysrq-reset-seq");
> > +     struct device_node *np __free(device_node) =
> > +             of_find_node_by_path("/chosen/linux,sysrq-reset-seq");
> > +
> >       if (!np) {
> >               pr_debug("No sysrq node found");
> >               return;
> > @@ -781,8 +782,6 @@ static void sysrq_of_get_keyreset_config(void)
> >
> >       /* Get reset timeout if any. */
> >       of_property_read_u32(np, "timeout-ms", &sysrq_reset_downtime_ms);
> > -
> > -     of_node_put(np);
> >  }
> >  #else
> >  static void sysrq_of_get_keyreset_config(void)
>
> Also, this change really makes no sense at all, the pointer never goes
> out of scope except when the function is over, at the bottom.  So why
> make this complex change at all for no benefit?
>
> In other words, properly understand the change you are making and only
> make it if it actually makes sense.  It does not make any sense here,
> right?
>
> thanks,
>
> greg k-h



-- 
Kind regards,
Roman Storozhenko