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

[Petr Mladek <pmladek@suse.com>]

(and really add Andy)

On Wed 2021-11-03 15:50:04, John Ogness wrote:
> 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.

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.

Adding Andy into Cc.

> 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")

Yes, I consider this to be the culprit.

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

Please add the Fixes tag and the following into the commit message:

Cc: stable@vger.kernel.org # v5.5+

Best Regards,
Petr