From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 10 May 2001 17:15:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 10 May 2001 17:15:13 -0400 Received: from penguin.e-mind.com ([195.223.140.120]:13101 "EHLO penguin.e-mind.com") by vger.kernel.org with ESMTP id ; Thu, 10 May 2001 17:14:58 -0400 Date: Thu, 10 May 2001 23:13:00 +0200 From: Andrea Arcangeli To: Andi Kleen Cc: Alan Cox , Ulrich.Weigand@de.ibm.com, linux-kernel@vger.kernel.org, schwidefsky@de.ibm.com Subject: Re: Deadlock in 2.2 sock_alloc_send_skb? Message-ID: <20010510231300.W848@athlon.random> In-Reply-To: <20010510193047.A22970@gruyere.muc.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20010510193047.A22970@gruyere.muc.suse.de>; from ak@suse.de on Thu, May 10, 2001 at 07:30:47PM +0200 X-GnuPG-Key-URL: http://e-mind.com/~andrea/aa.gnupg.asc X-PGP-Key-URL: http://e-mind.com/~andrea/aa.asc Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 10, 2001 at 07:30:47PM +0200, Andi Kleen wrote: > On Thu, May 10, 2001 at 01:57:49PM +0100, Alan Cox wrote: > > > If that happens, and the socket uses GFP_ATOMIC allocation, the while (1) > > > loop in sock_alloc_send_skb() will endlessly spin, without ever calling > > > schedule(), and all the time holding the kernel lock ... > > > > If the socket is using GFP_ATOMIC allocation it should never loop. That is > > -not-allowed-. > > It is just not clear why any socket should use GFP_ATOMIC. I can understand > it using GFP_BUFFER e.g. for nbd, but GFP_ATOMIC seems to be rather radical > and fragile. side note, the only legal use of GFP_ATOMIC in sock_alloc_send_skb is with noblock set and fallback zero, remeber GFP_BUFFER will sleep, it may not sleep in vanilla 2.2.19 but the necessary lowlatency hooks in the memory balancing that for example I have on my 2.2 tree will make it to sleep. The patch self contained looks perfect (I didn't checked that the callers are happy with a -ENOMEM errorcode though), if alloc_skb() failed that's a plain -ENOMEM. The caller must _not_ try again, they must take a recovery fail path instead. Andrea