On Tue, Nov 14, 2023 at 03:35:58PM +0100, 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.
One nit-pick below, otherwise Reviewed-by: Andy Shevchenko andriy.shevchenko@linux.intel.com
...
/* Loop starting from the root node to the current node. */ for (depth = fwnode_count_parents(fwnode); depth >= 0; depth--) {
struct fwnode_handle *__fwnode =fwnode_get_nth_parent(fwnode, depth);
/** Only get a reference for other nodes (ie parents node).
"parent's node" (doesn't look right)? Or "parent nodes"?
* fwnode refcount may be 0 here.*/struct fwnode_handle *__fwnode = depth ?fwnode_get_nth_parent(fwnode, depth) : fwnode;buf = string(buf, end, fwnode_get_name_prefix(__fwnode), default_str_spec); buf = string(buf, end, fwnode_get_name(__fwnode), default_str_spec);
fwnode_handle_put(__fwnode);
if (depth)fwnode_handle_put(__fwnode);