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. -- With Best Regards, Andy Shevchenko
