linux-kernel - RE: [PATCH v12 net-next 1/1] hv_sock: introduce Hyper-V Sockets

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Message-ID: <CO2PR03MB2182CC1DA2804F09D8D77A70BF220@CO2PR03MB2182.namprd03.prod.outlook.com>
Date:	Tue, 28 Jun 2016 09:59:21 +0000
From:	Dexuan Cui <decui@...rosoft.com>
To:	David Miller <davem@...emloft.net>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"vkuznets@...hat.com" <vkuznets@...hat.com>,
	"cavery@...hat.com" <cavery@...hat.com>,
	KY Srinivasan <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	"joe@...ches.com" <joe@...ches.com>
Subject: RE: [PATCH v12 net-next 1/1] hv_sock: introduce Hyper-V Sockets

> From: David Miller [mailto:davem@...emloft.net]
> Sent: Tuesday, June 28, 2016 17:34
> To: Dexuan Cui <decui@...rosoft.com>
> Cc: gregkh@...uxfoundation.org; netdev@...r.kernel.org; linux-
> kernel@...r.kernel.org; devel@...uxdriverproject.org; olaf@...fle.de;
> apw@...onical.com; jasowang@...hat.com; vkuznets@...hat.com;
> cavery@...hat.com; KY Srinivasan <kys@...rosoft.com>; Haiyang Zhang
> <haiyangz@...rosoft.com>; joe@...ches.com
> Subject: Re: [PATCH v12 net-next 1/1] hv_sock: introduce Hyper-V Sockets
> 
> From: Dexuan Cui <decui@...rosoft.com>
> Date: Fri, 24 Jun 2016 07:45:24 +0000
> 
> > +	while ((ret = vmalloc(size)) == NULL)
> > +		ssleep(1);
> 
> This is completely, and entirely, unacceptable.
> 
> If the allocation fails, you return an error and release
> your resources.
> 
> You don't just loop forever waiting for it to succeed.

Hi David,
I agree this is ugly...

The idea here is: IMO the syscalls sys_read()/write() shoudn't return
-ENOMEM, so I have to make sure the buffer allocation succeeds?

I tried to use kmalloc with __GFP_NOFAIL, but I hit a warning in 
in mm/page_alloc.c:
WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1));

What error code do you think I should return? 
EAGAIN, ERESTARTSYS, or something else?

May I have your suggestion? Thanks!

-- Dexuan