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

[Herve Codina]

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