From: Oliver Neukum <oneukum@suse.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: linux-usb@vger.kernel.org
Subject: Re: [RFC]extension of the anchor API
Date: Wed, 14 Apr 2021 10:12:01 +0200 [thread overview]
Message-ID: <30abed362c4b2e6af33078505ac9985389ad39bb.camel@suse.com> (raw)
In-Reply-To: <20210412150628.GA1420451@rowland.harvard.edu>
Am Montag, den 12.04.2021, 11:06 -0400 schrieb Alan Stern:
> On Mon, Apr 12, 2021 at 11:58:16AM +0200, Oliver Neukum wrote:
> > That presumes that the URBs will finish in order. I don't think such
> > an assumption can be made.
>
> I don't understand -- I can't detect any such presumption.
OK, this shows that I am bad at explaining.
>
> As far as I can tell, the only reason for maintaining the URBs in any
> particular order on the anchor list is so that usb_kill_anchored_urbs
> and usb_poison_anchored_urbs can kill them in reverse order of
> submission. THat's why the current code moves completed URBs to the end
> of the list.
No longer strictly true, as the API has a call to submit everything
on an anchor, but I think it boils down to the same thing.
> If you keep a pointer to the most recently submitted URB, killing them
> easy enough to do. Start with that URB, then go backward through the
> list (wrapping to the end when you reach the beginning of the list).
Yes, but that supposes that the next on the list has not been
resubmitted _before_ the one after it.
If you do not keep the list ordered, but in the initial order,
we can have the situation that A (happens most recently submitted)
is followed by B and C, but C was submitted before B.
>
> The order in which the URBs complete doesn't matter, because trying to
> unlink a completed URB won't cause any harm.
As long as it stays completed.
> The only assumption here
> is that URBs get submitted in the list's order (possibly circularly) --
> this should always be true.
I am afraid we cannot guarantee that. It might intuitively seem so,
but nothing guarantees that all URBs are going to the same endpoint.
Regards
Oliver
next prev parent reply other threads:[~2021-04-14 8:12 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-25 11:03 [RFC]extension of the anchor API Oliver Neukum
2021-03-25 15:06 ` Alan Stern
2021-03-25 16:04 ` Oliver Neukum
2021-03-25 18:38 ` Alan Stern
2021-04-08 9:23 ` Oliver Neukum
2021-04-08 15:07 ` Alan Stern
2021-04-12 9:58 ` Oliver Neukum
2021-04-12 15:06 ` Alan Stern
2021-04-14 8:12 ` Oliver Neukum [this message]
2021-04-14 14:56 ` Alan Stern
2021-04-15 11:23 ` Oliver Neukum
2021-04-15 15:18 ` Alan Stern
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