linux-kernel - Re: [PATCH] usb: yurex: Rearrange code not to need GFP

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Date:   Mon, 21 Sep 2020 15:00:16 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Pavel Machek <pavel@...x.de>
Cc:     gregkh@...uxfoundation.org, stern@...land.harvard.edu,
        johan@...nel.org, gustavoars@...nel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: yurex: Rearrange code not to need GFP_ATOMIC

Am Montag, den 21.09.2020, 14:52 +0200 schrieb Pavel Machek:
> Hi!

> > 
> > Task goes to TASK_INTERRUPTIBLE
> > 
> > >  	if (retval >= 0)
> > >  		timeout = schedule_timeout(YUREX_WRITE_TIMEOUT);
> > 
> > Task turns into Sleeping Beauty until timeout
> 
> Is there way to do the allocations for submit_urb before the

No. In theory you do not even know which HC will get the URB.
Preallocating resources is impossible. I do consider this a
design bug in the usbcore API.

> prepare_to_wait? GFP_ATOMIC would be nice to avoid... and doing
> GFP_ATOMIC from normal process context just because of task_state
> seems ... wrong.

Well, then you will need to change the rest of the logic
and use a struct completion. Give the age and practical
relevance of the driver I would recommend against making
such drastic changes and let it just be in its awkward
but correct state.

	Regards
		Oliver