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

Sakari Ailus
2021-11-04T12:45:50Z

Hi Petr, John,

On Wed, Nov 03, 2021 at 04:47:44PM +0100, Petr Mladek wrote:
> 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.

That holds for OF and swnode already, ACPI was an exception to this.

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

Fair enough.

> >
> > 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+

I'll use that in v2.

--
Regards,

Sakari Ailus