From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f177.google.com (mail-pd0-f177.google.com [209.85.192.177]) by kanga.kvack.org (Postfix) with ESMTP id 5C60E6B003A for ; Wed, 16 Apr 2014 01:49:50 -0400 (EDT) Received: by mail-pd0-f177.google.com with SMTP id y10so10313036pdj.36 for ; Tue, 15 Apr 2014 22:49:50 -0700 (PDT) Received: from ipmail06.adl6.internode.on.net (ipmail06.adl6.internode.on.net. [2001:44b8:8060:ff02:300:1:6:6]) by mx.google.com with ESMTP id l1si12077334paw.69.2014.04.15.22.49.48 for ; Tue, 15 Apr 2014 22:49:49 -0700 (PDT) Date: Wed, 16 Apr 2014 15:49:42 +1000 From: Dave Chinner Subject: Re: [PATCH 13/19] MM: set PF_FSTRANS while allocating per-cpu memory to avoid deadlock. Message-ID: <20140416054942.GD15995@dastard> References: <20140416033623.10604.69237.stgit@notabene.brown> <20140416040336.10604.67456.stgit@notabene.brown> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140416040336.10604.67456.stgit@notabene.brown> Sender: owner-linux-mm@kvack.org List-ID: To: NeilBrown Cc: linux-mm@kvack.org, linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, xfs@oss.sgi.com On Wed, Apr 16, 2014 at 02:03:36PM +1000, NeilBrown wrote: > lockdep reports a locking chain > > sk_lock-AF_INET --> rtnl_mutex --> pcpu_alloc_mutex > > As sk_lock may be needed to reclaim memory, allowing that > reclaim while pcu_alloc_mutex is held can lead to deadlock. > So set PF_FSTRANS while it is help to avoid the FS reclaim. > > pcpu_alloc_mutex can be taken when rtnl_mutex is held: > > [] pcpu_alloc+0x49/0x960 > [] __alloc_percpu+0xb/0x10 > [] loopback_dev_init+0x17/0x60 > [] register_netdevice+0xec/0x550 > [] register_netdev+0x15/0x30 > > Signed-off-by: NeilBrown This looks like a workaround to avoid passing a gfp mask around to describe the context in which the allocation is taking place. Whether or not that's the right solution, I can't say, but spreading this "we can turn off all reclaim of filesystem objects" mechanism all around the kernel doesn't sit well with me... And, again, PF_FSTRANS looks plainly wrong in this code - it sure isn't a fs transaction context we are worried about here... -- Dave Chinner david@fromorbit.com -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org