Subject: Re: [PATCH v3 02/10] mtd: powernv_flash: Lock around concurrent access to OPAL

From: Balbir Singh <[email-masked]>
Date: Mon, 17 Jul 2017 19:29:14 +1000

On Mon, 2017-07-17 at 17:55 +1000, Cyril Bur wrote:
> On Mon, 2017-07-17 at 17:34 +1000, Balbir Singh wrote:
> > On Wed, 2017-07-12 at 14:22 +1000, Cyril Bur wrote:
> > > OPAL can only manage one flash access at a time and will return an
> > > OPAL_BUSY error for each concurrent access to the flash. The simplest
> > > way to prevent this from happening is with a mutex.
> > > 
> > > Signed-off-by: Cyril Bur <[email-masked]>
> > > ---
> > 
> > Should the mutex_lock() be mutex_lock_interruptible()? Are we OK waiting on
> > the mutex while other operations with the lock are busy?
> > 
> 
> This is a good question. My best interpretation is that
> _interruptible() should be used when you'll only be coming from a user
> context. Which is mostly true for this driver, however, MTD does
> provide kernel interfaces, so I was hesitant, there isn't a great deal
> of use of _interruptible() in drivers/mtd. 
> 
> Thoughts?

What are the kernel interfaces (I have not read through mtd in detail)?
I would still like to see us not blocked in mutex_lock() across threads
for parallel calls, one option is to use mutex_trylock() and return if
someone already holds the mutex with -EBUSY, but you'll need to evaluate
what that means for every call.

Balbir Singh.