Re: [PATCH] mfd: max77620: Avoid regmap mutex deadlock in power-off handler

[Mark Brown]

On Wed, May 20, 2026 at 05:19:00PM +0100, Lee Jones wrote:
> On Wed, 20 May 2026, Diogo Ivo wrote:

> > This patch was motivated by the Sashiko review I got in [1]. Its point
> > here is that there is a possibility for a deadlock scenario in which
> > a secondary CPU obtains the mutex for the regmap and then smp_send_stop()
> > is called before this secondary CPU gets a chance to release the mutex,
> > making it so that when the primary CPU tries to acquire it to issue the
> > write it hangs. Is there something that I am misunderstanding here?
> > 

> It's my understanding that using the Regmap wrappers _prevents_ locking
> issues, rather than causes them.

In the case where the CPU is being powered off during a regmap write
there is a potential issue - as Diogo says if we're in the middle of
holding the lock and we power off the CPU that owns the lock then it
will never be able to release the lock.  I would expect the same issue
to apply to a bus like I2C or SPI though, they'll hold a lock while
they're in the middle of doing bus I/O unless you use some special API.

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