Re: [PATCH 1/1] driver core: Avoid using fwnode in __fwnode_link_del()

[Saravana Kannan]

On Fri, Nov 10, 2023 at 9:01 AM Herve Codina <herve.codina@xxxxxxxxxxx> 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>
>   ? refcount_warn_saturate+0xe5/0x110
>   ? __warn+0x81/0x130
>   ? refcount_warn_saturate+0xe5/0x110
>   ? report_bug+0x191/0x1c0
>   ? srso_alias_return_thunk+0x5/0x7f
>   ? prb_read_valid+0x1b/0x30
>   ? handle_bug+0x3c/0x80
>   ? exc_invalid_op+0x17/0x70
>   ? asm_exc_invalid_op+0x1a/0x20
>   ? refcount_warn_saturate+0xe5/0x110
>   kobject_get+0x68/0x70
>   of_node_get+0x1e/0x30
>   of_fwnode_get+0x28/0x40
>   fwnode_full_name_string+0x34/0x90
>   fwnode_string+0xdb/0x140
>   vsnprintf+0x17b/0x630
>   va_format.isra.0+0x71/0x130
>   vsnprintf+0x17b/0x630
>   vprintk_store+0x162/0x4d0
>   ? srso_alias_return_thunk+0x5/0x7f
>   ? srso_alias_return_thunk+0x5/0x7f
>   ? srso_alias_return_thunk+0x5/0x7f
>   ? try_to_wake_up+0x9c/0x620
>   ? rwsem_mark_wake+0x1b2/0x310
>   vprintk_emit+0xe4/0x2b0
>   _printk+0x5c/0x80
>   __dynamic_pr_debug+0x131/0x160
>   ? srso_alias_return_thunk+0x5/0x7f
>   __fwnode_link_del+0x25/0xa0
>   fwnode_links_purge+0x39/0xb0
>   of_node_release+0xd9/0x180
>   kobject_put+0x7b/0x190
>   ...
>
> Indeed, an of_node is destroyed and so, of_node_release() is called
> because the of_node refcount reached 0.
> of_node_release() calls fwnode_links_purge() to purge the links and
> ended with __fwnode_link_del() calls.
> __fwnode_link_del calls pr_debug() to print the fwnodes (of_nodes)
> involved in the link and so this call is done while one of them is no
> more available (ie the one related to the of_node_release() call)
>
> Remove the pr_debug() call to avoid the use of the links fwnode while
> destroying the fwnode itself.
>
> Fixes: ebd6823af378 ("driver core: Add debug logs when fwnode links are added/deleted")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Herve Codina <herve.codina@xxxxxxxxxxx>
> ---
>  drivers/base/core.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index f4b09691998e..62088c663014 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -109,8 +109,6 @@ int fwnode_link_add(struct fwnode_handle *con, struct fwnode_handle *sup)
>   */
>  static void __fwnode_link_del(struct fwnode_link *link)
>  {
> -       pr_debug("%pfwf Dropping the fwnode link to %pfwf\n",
> -                link->consumer, link->supplier);

Valid issue, but a NACK for the patch.

The pr_debug has been very handy, so I don't want to delete it. Also,
the fwnode link can't get deleted before the supplier/consumer. If it
is, I need to take a closer look as I'd expect the list_del() to cause
corruption. My guess is that the %pfwf is traversing stuff that's
causing an issue. But let me take a closer look next week when I'll be
at LPC.

-Saravana

>         list_del(&link->s_hook);
>         list_del(&link->c_hook);
>         kfree(link);
> --
> 2.41.0
>