linux-kernel - Re: [PATCH] usb/mos7720: process deferred urbs in a workqueue

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Message-ID: <20201105001307.lelve65nif344cfs@linux-p48b.lan>
Date:   Wed, 4 Nov 2020 16:13:07 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Johan Hovold <johan@...nel.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH] usb/mos7720: process deferred urbs in a workqueue

On Wed, 04 Nov 2020, Johan Hovold wrote:

>Hmm. I took at closer look at the parport code and it seems the current
>implementation is already racy but that removing the tasklet is going to
>widen that that window.
>
>Those register writes in restore() should be submitted before any
>later requests. Perhaps setting a flag and flushing the work in
>parport_prologue() could work?

Ah, I see and agree. Considering work is only deferred from restore_state()
I don't even think we need a flag, no? We can let parport_prologue()
just flush_work() unconditionally (right before taking the disc_mutex)
which for the most part will be idle anyway. The flush_work() also becomes
saner now that we'll stop rescheduling work in send_deferred_urbs().

Also, but not strictly related to this. What do you think of deferring all
work in write_parport_reg_nonblock() unconditionally? I'd like to avoid
that mutex_trylock() because eventually I'll be re-adding a warn in the
locking code, but that would also simplify the code done here in the
nonblocking irq write. I'm not at all familiar with parport, but I would
think that restore_state context would not care.

>On the other hand, the restore() implementation looks broken in that it
>doesn't actually restore the provided state. I'll go fix that up.

How did this thing ever work?

Thanks,
Davidlohr