linux-kernel - Re: [PATCH v5 1/3] PM: wakeup: Add routine to help fetch wakeup source object.

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Message-ID: <CAJZ5v0i58p-GsswzMGEsgD5OXDqJ_G5zXDYf8jq8JJbWxZv+nQ@mail.gmail.com>
Date:   Mon, 19 Aug 2019 10:20:11 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Ran Wang <ran.wang_1@....com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Leo Li <leoyang.li@....com>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Pavel Machek <pavel@....cz>, Biwen Li <biwen.li@....com>,
        Len Brown <len.brown@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v5 1/3] PM: wakeup: Add routine to help fetch wakeup
 source object.

On Mon, Aug 19, 2019 at 10:15 AM Ran Wang <ran.wang_1@....com> wrote:
>
> Hi Rafael,
>
> On Monday, August 05, 2019 17:59, Rafael J. Wysocki wrote:
> >
> > On Wednesday, July 24, 2019 9:47:20 AM CEST Ran Wang wrote:
> > > Some user might want to go through all registered wakeup sources and
> > > doing things accordingly. For example, SoC PM driver might need to do
> > > HW programming to prevent powering down specific IP which wakeup
> > > source depending on. So add this API to help walk through all
> > > registered wakeup source objects on that list and return them one by one.
> > >
> > > Signed-off-by: Ran Wang <ran.wang_1@....com>
> > > ---
> > > Change in v5:
> > >     - Update commit message, add decription of walk through all wakeup
> > >     source objects.
> > >     - Add SCU protection in function wakeup_source_get_next().
> > >     - Rename wakeup_source member 'attached_dev' to 'dev' and move it
> > up
> > >     (before wakeirq).
> > >
> > > Change in v4:
> > >     - None.
> > >
> > > Change in v3:
> > >     - Adjust indentation of *attached_dev;.
> > >
> > > Change in v2:
> > >     - None.
> > >
> > >  drivers/base/power/wakeup.c | 24 ++++++++++++++++++++++++
> > >  include/linux/pm_wakeup.h   |  3 +++
> > >  2 files changed, 27 insertions(+)
> > >
> > > diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
> > > index ee31d4f..2fba891 100644
> > > --- a/drivers/base/power/wakeup.c
> > > +++ b/drivers/base/power/wakeup.c
> > > @@ -14,6 +14,7 @@
> > >  #include <linux/suspend.h>
> > >  #include <linux/seq_file.h>
> > >  #include <linux/debugfs.h>
> > > +#include <linux/of_device.h>
> > >  #include <linux/pm_wakeirq.h>
> > >  #include <trace/events/power.h>
> > >
> > > @@ -226,6 +227,28 @@ void wakeup_source_unregister(struct
> > wakeup_source *ws)
> > >     }
> > >  }
> > >  EXPORT_SYMBOL_GPL(wakeup_source_unregister);
> > > +/**
> > > + * wakeup_source_get_next - Get next wakeup source from the list
> > > + * @ws: Previous wakeup source object, null means caller want first one.
> > > + */
> > > +struct wakeup_source *wakeup_source_get_next(struct wakeup_source
> > > +*ws) {
> > > +   struct list_head *ws_head = &wakeup_sources;
> > > +   struct wakeup_source *next_ws = NULL;
> > > +   int idx;
> > > +
> > > +   idx = srcu_read_lock(&wakeup_srcu);
> > > +   if (ws)
> > > +           next_ws = list_next_or_null_rcu(ws_head, &ws->entry,
> > > +                           struct wakeup_source, entry);
> > > +   else
> > > +           next_ws = list_entry_rcu(ws_head->next,
> > > +                           struct wakeup_source, entry);
> > > +   srcu_read_unlock(&wakeup_srcu, idx);
> > > +
> >
> > This is incorrect.
> >
> > The SRCU cannot be unlocked until the caller of this is done with the object
> > returned by it, or that object can be freed while it is still being accessed.
>
> Thanks for the comment. Looks like I was not fully understanding your point on
> v4 discussion. So I will implement 3 APIs by referring wakeup_sources_stats_seq_start/next/stop()
>
> > Besides, this patch conflicts with some general wakeup sources changes in the
> > works, so it needs to be deferred and rebased on top of those changes.
>
> Could you please tell me which is the right code base I should developing on?
> I just tried applying v5 patch on latest git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git branch master (d1abaeb Linux 5.3-rc5)
> and no conflict encountered.

It is better to use the most recent -rc from Linus (5.3-rc5 as of
today) as the base unless your patches depend on some changes that are
not in there.