linux-kernel - Re: USB device cannot be reconnected and khubd "blocked for more than 120 seconds"

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Message-ID: <CA+55aFzZ1NJz34r99N7+mU4CN5Ju4QpHrDoWv5Kbd5-Z4QzgaA@mail.gmail.com>
Date:	Tue, 15 Jan 2013 12:18:01 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Ming Lei <ming.lei@...onical.com>,
	Alex Riesen <raa.lkml@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Jens Axboe <axboe@...nel.dk>,
	USB list <linux-usb@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: USB device cannot be reconnected and khubd "blocked for more than
 120 seconds"

On Tue, Jan 15, 2013 at 10:32 AM, Tejun Heo <tj@...nel.org> wrote:
>
> I think the root problem here, apart from request_module() from block
> - which is a bit nasty but making that part completely async would too
> be quite nasty albeit in a different way - is that
> async_synchronize_full() is way too indescriminate.  It's something
> only suitable for things like the end of system init.
>
> I'm wondering whether what we need is a rudimentray nesting like the
> following.

I think that is a good solution if it works, but look out: we need to
synchronize across *all* domains, not just the default one.  The sd.c
code, for example, uses its own "scsi_sd_probe_domain" for example,
and we *do* want to synchronize with it.

Can you do that with your suggested interface (ie it would have to be
a *global* sequence number).

               Linus
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