Re: [PATCH 0/3] Get device's parent from parent field, fix sleeping IRQs disabled

[John Ogness <john.ogness@linutronix.de>]

added CC: printk maintainer (Petr Mladek)

On 2021-11-03, Sakari Ailus <sakari.ailus@linux.intel.com> 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.

Well, before my work it was vprintk_emit() that was disabling local
interrupts. So this has always been broken.

Really it should be:

Fixes: 3bd32d6a2ee6 ("lib/vsprintf: Add %pfw conversion specifier for
printing fwnode names")

Regardless, the fix should go into 5.10 and 5.14 stables.

John Ogness