linux-kernel - Re: [PATCH v2 2/2] of: dynamic: flush devlinks workqueue before destroying the changeset

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Message-ID: <17baf0c5e1ce19a1bc930fd439c27d9ef8cbe6a1.camel@gmail.com>
Date: Wed, 21 Feb 2024 08:13:05 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: Saravana Kannan <saravanak@...gle.com>
Cc: Rob Herring <robh@...nel.org>, Nuno Sa <nuno.sa@...log.com>, Greg
 Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
 <rafael@...nel.org>, Frank Rowand <frowand.list@...il.com>, Andy Shevchenko
 <andriy.shevchenko@...ux.intel.com>,  Daniel Scally <djrscally@...il.com>,
 Heikki Krogerus <heikki.krogerus@...ux.intel.com>, Sakari Ailus
 <sakari.ailus@...ux.intel.com>, Len Brown <lenb@...nel.org>, 
 linux-acpi@...r.kernel.org, devicetree@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH v2 2/2] of: dynamic: flush devlinks workqueue before
 destroying the changeset

On Tue, 2024-02-20 at 16:39 -0800, Saravana Kannan wrote:
> On Wed, Feb 14, 2024 at 4:48 AM Nuno Sá <noname.nuno@...il.com> wrote:
> > 
> > On Tue, 2024-02-13 at 19:44 -0800, Saravana Kannan wrote:
> > > On Tue, Feb 13, 2024 at 6:57 AM Nuno Sá <noname.nuno@...il.com> wrote:
> > > > 
> > > > On Tue, 2024-02-13 at 08:51 -0600, Rob Herring wrote:
> > > > > On Mon, Feb 12, 2024 at 01:10:27PM +0100, Nuno Sá wrote:
> > > > > > On Mon, 2024-02-05 at 13:09 +0100, Nuno Sa wrote:
> > > > > > > Device links will drop their supplier + consumer refcounts
> > > > > > > asynchronously. That means that the refcount of the of_node attached
> > > > > > > to
> > > > > > > these devices will also be dropped asynchronously and so we cannot
> > > > > > > guarantee the DT overlay assumption that the of_node refcount must be
> > > > > > > 1 in
> > > > > > > __of_changeset_entry_destroy().
> > > > > > > 
> > > > > > > Given the above, call the new fwnode_links_flush_queue() helper to
> > > > > > > flush
> > > > > > > the devlink workqueue so we can be sure that all links are dropped
> > > > > > > before
> > > > > > > doing the proper checks.
> > > > > > > 
> > > > > > > Signed-off-by: Nuno Sa <nuno.sa@...log.com>
> > > > > > > ---
> > > > > > >  drivers/of/dynamic.c | 8 ++++++++
> > > > > > >  1 file changed, 8 insertions(+)
> > > > > > > 
> > > > > > > diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
> > > > > > > index 3bf27052832f..b7153c72c9c9 100644
> > > > > > > --- a/drivers/of/dynamic.c
> > > > > > > +++ b/drivers/of/dynamic.c
> > > > > > > @@ -14,6 +14,7 @@
> > > > > > >  #include <linux/slab.h>
> > > > > > >  #include <linux/string.h>
> > > > > > >  #include <linux/proc_fs.h>
> > > > > > > +#include <linux/fwnode.h>
> > > > > > > 
> > > > > > >  #include "of_private.h"
> > > > > > > 
> > > > > > > @@ -518,6 +519,13 @@ EXPORT_SYMBOL(of_changeset_create_node);
> > > > > > > 
> > > > > > >  static void __of_changeset_entry_destroy(struct of_changeset_entry
> > > > > > > *ce)
> > > > > > >  {
> > > > > > > + /*
> > > > > > > +  * device links drop their device references (and hence their
> > > > > > > of_node
> > > > > > > +  * references) asynchronously on a dedicated workqueue Hence we
> > > > > > > need
> > > > > > > +  * to flush it to make sure everything is done before doing the
> > > > > > > below
> > > > > > > +  * checks.
> > > > > > > +  */
> > > > > > > + fwnode_links_flush_queue();
> > > > > > >   if (ce->action == OF_RECONFIG_ATTACH_NODE &&
> > > > > > >       of_node_check_flag(ce->np, OF_OVERLAY)) {
> > > > > > >           if (kref_read(&ce->np->kobj.kref) > 1) {
> > > > > > > 
> > > > > > 
> > > > > > Hi Rob and Frank,
> > > > > > 
> > > > > > Any way you could take a look at this and see if you're ok with the
> > > > > > change
> > > > > > in the
> > > > > > overlay code?
> > > > > > 
> > > > > > On the devlink side , we already got the ok from Rafael.
> > > > > 
> > > > > Didn't Saravana say he was going to look at this? As of yesterday, he's
> > > > > also a DT maintainer so deferring to him.
> > > > > 
> > > > 
> > > > Yeah, I did asked him but I guess he never had the time for it... Saravana,
> > > > could you please give some feedback on this? I think the most sensible part
> > > > is
> > > > on the devlink side but I assume this is not going to be merged without an
> > > > ack
> > > > from a DT maintainer...
> > > 
> > > Sorry for the delay Nuno. I'll get to this. I promise. This week is a bit
> > > busy.
> > > 
> > 
> > No worries. Just making sure it's not forgotten :)
> 
> Hi Nuno,
> 
> Thanks for nudging me about this issue.
> 
> I replied to a similar patch series that Herve sent out last year.
> Chose to reply to that because it had fewer issues to fix and Herve
> sent it out a while ago.

Ehehe, FWIW, I did sent it out before I believe:

https://lore.kernel.org/lkml/20231127-fix-device-links-overlays-v1-1-d7438f56d025@analog.com/

I just got no attention and it took some time until I got some feedback (I also
pushed for it with resends). If you follow the links in the cover, you'll see I first
started (and spotted the issue) the effort in May last year.

That said, I'm more than fine with whatever series is taken. I just care about the
problem being solved :)

- Nuno Sá