netdev - Re: [PATCH 01/12] usbnet: introduce usbnet 3 command helpers

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Date:	Wed, 10 Oct 2012 13:39:47 +0200
From:	Oliver Neukum <oneukum@...e.de>
To:	David Laight <David.Laight@...lab.com>
Cc:	Ming Lei <ming.lei@...onical.com>,
	"David S. Miller" <davem@...emloft.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	netdev@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH 01/12] usbnet: introduce usbnet 3 command helpers

On Wednesday 10 October 2012 12:25:58 David Laight wrote:
> > On Wed, Oct 10, 2012 at 6:08 PM, Oliver Neukum <oneukum@...e.de> wrote:
> > 
> > > A reset always applies to the whole device. Resets are used in error
> > > handling of block devices (storage and uas). If you reset a device,
> > > pre_reset() and post_reset() of all interfaces need to be called. So they
> > > are part of the SCSI error handler. SCSI error handlers can allocate memory
> > > only with GFP_NOIO (or GFP_ATOMIC) because any IO for paging
> > > can cause the SCSI layer to wait for the error handling to finish. The error
> > > handling can only finish when pre/post_reset() have finished. Catch-22
> > 
> > IMO, it is not practical to obey the rule for drivers, because driver may
> > call many other kernel component API which may allocate memory
> > via GFP_KERNEL in the path easily.
> 
> What about the error handler/sleep/resume code calling into the
> memory allocator to indicate that all allocates be GFP_NOIO until
> it calls back to indicate that the restricted path is complete.

This seems to be a very complex scheme.

> Might be a per-cpu count?

No. The handlers may sleep and switch CPUs.

	Regards
		Oliver

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