linux-kernel - Re: [PATCH v3 1/1] lib/vsprintf: Fix %pfwf when current node refcount == 0

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Date:   Wed, 6 Dec 2023 11:46:43 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Herve Codina <herve.codina@...tlin.com>
Cc:     Saravana Kannan <saravanak@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        linux-kernel@...r.kernel.org,
        Allan Nielsen <allan.nielsen@...rochip.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Steen Hegelund <steen.hegelund@...rochip.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v3 1/1] lib/vsprintf: Fix %pfwf when current node
 refcount == 0

On Tue 2023-11-14 16:26:55, Herve Codina wrote:
> A refcount issue can appeared in __fwnode_link_del() due to the
> pr_debug() call:
>   WARNING: CPU: 0 PID: 901 at lib/refcount.c:25 refcount_warn_saturate+0xe5/0x110
>   Call Trace:
>   <TASK>
>   ...
>   of_node_get+0x1e/0x30
>   of_fwnode_get+0x28/0x40
>   fwnode_full_name_string+0x34/0x90
>   fwnode_string+0xdb/0x140
>   ...
>   vsnprintf+0x17b/0x630
>   ...
>   __fwnode_link_del+0x25/0xa0
>   fwnode_links_purge+0x39/0xb0
>   of_node_release+0xd9/0x180
>   ...
> 
> Indeed, an fwnode (of_node) is being destroyed and so, of_node_release()
> is called because the of_node refcount reached 0.
> >From of_node_release() several function calls are done and lead to
> a pr_debug() calls with %pfwf to print the fwnode full name.
> The issue is not present if we change %pfwf to %pfwP.
> 
> To print the full name, %pfwf iterates over the current node and its
> parents and obtain/drop a reference to all nodes involved.
> 
> In order to allow to print the full name (%pfwf) of a node while it is
> being destroyed, do not obtain/drop a reference to this current node.
> 
> Fixes: a92eb7621b9f ("lib/vsprintf: Make use of fwnode API to obtain node names and separators")
> Cc: stable@...r.kernel.org
> Signed-off-by: Herve Codina <herve.codina@...tlin.com>
> Reviewed-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

I have pushed the fix into printk/linux.git, branch for-6.8.

Please, let me know if you would prefer to push this into 6.7.

The "Fixes:" tag points to a pretty old commit from v5.5 so
it does not look like a super urgent fix. And I always
prefer when fixes spend some time in linux-next.

Best Regards,
Petr