On Tue, Nov 14, 2023 at 12:04:56PM +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> ? 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 ...
Please, do not put so many unrelated lines of backtrace in the commit message. Leave only the important ones (the Submitting Patches document suggests some like ~3-5 lines only).
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.