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
>
