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List: linux-kernel
Subject: Re: [PATCH] usb: cdc-wdm: close race between read and workqueue
From: Oliver Neukum <oneukum () suse ! com>
Date: 2024-04-15 10:14:48
Message-ID: c35f98be-23a3-41c3-bee5-f394ce504545 () suse ! com
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On 15.04.24 11:26, Bjørn Mork wrote:
> Oliver Neukum <oneukum@suse.com> writes:
> > On 15.04.24 08:47, Bjørn Mork wrote:
> >
> > > urb from service_outstanding_interrupt(). That's why it was added. See
> > > the explanation Robert wrote when introducing it:
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/usb/class/cdc-wdm.c?id=c1da59dad0ebd3f9bd238f3fff82b1f7ffda7829
> > >
> >
> > Well, the explanation is correct in that we must read
> > data available. However, if the RESPONDING flag is set
> > and the URB submitted, we are already doing so.
>
> Sounds reasonable. Except that the bug proves we didn't.
Why? I am afraid I do not get that part.
> If you are right that service_outstanding_interrupt can race againts
> itself (and I don't doubt that), then I guess this could also happen
> between failure to submit the URB and clearing the flag?
Yes, it can. In fact in this case the behavior should not change.
I am afraid we have a misunderstanding. It seems to me that in the
unchanged driver the result of service_outstanding_interrupt()
is undefined.
Please explain.
Regards
Oliver
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