On Wed, Nov 03, 2021 at 04:47:44PM +0100, Petr Mladek wrote: > On Wed 2021-11-03 15:50:04, John Ogness wrote: > > On 2021-11-03, Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> wrote: > > > This set changes getting fwnode's parent on ACPI fwnode so it no longer > > > needs a semaphore, using struct acpi_device->parent field instead of > > > calling acpi_get_parent(). The semaphore is being acquired when the > > > device's full path is printed which now takes place local IRQs disabled: > > > > > > --------8<------------------------ > > > BUG: sleeping function called from invalid context at kernel/locking/semaphore.c:163 > > > > > > ... > > > > > > Call Trace: > > > <TASK> > > > dump_stack_lvl+0x57/0x7d > > > __might_resched.cold+0xf4/0x12f > > > down_timeout+0x21/0x70 > > > acpi_os_wait_semaphore+0x63/0x180 > > > acpi_ut_acquire_mutex+0x123/0x1ba > > > acpi_get_parent+0x30/0x71 > > > acpi_node_get_parent+0x64/0x90 > > > ? lock_acquire+0x1a0/0x300 > > > fwnode_count_parents+0x6d/0xb0 > > > fwnode_full_name_string+0x18/0x90 > > > fwnode_string+0xd7/0x140 > > > vsnprintf+0x1ec/0x4f0 > > > va_format.constprop.0+0x6a/0x130 > > > vsnprintf+0x1ec/0x4f0 > > > vprintk_store+0x271/0x5a0 > > > ? rcu_read_lock_sched_held+0x12/0x70 > > > ? lock_release+0x228/0x310 > > > ? acpi_initialize_hp_context+0x50/0x50 > > > vprintk_emit+0xd5/0x340 > > > _printk+0x58/0x6f > > ... > > > --------8<------------------------ > > > > > > I guess one could argue it wasn't great to begin with that getting > > > fwnode's parent required a semaphore to begin with, nevertheless John's > > > patch made it a concrete problem. Added Cc: stable, too. > > It looks like a generic problem. > > If I get it properly, we should make sure that any struct > fwnode_operations implementation will _not_ use sleeping locks in > the .get_parent() callback. Or anything that is called indirectly > from from vsprintf. Not sure how I may help here, but if there is a requirement to all *printf() to be non-sleepable, then yes, this should be done in that way. I'm not sure if every single %p extension does this... It may require to update fwnode (source code) documentation to reflect the requirement. Also might_sleep() / migth_sleep_if() in the API calls may shed a light on (potential) issues. -- With Best Regards, Andy Shevchenko
