From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id E74631A01DE for ; Thu, 27 Nov 2014 02:17:54 +1100 (AEDT) Date: Wed, 26 Nov 2014 17:17:29 +0200 From: "Michael S. Tsirkin" To: David Hildenbrand Subject: Re: [RFC 0/2] Reenable might_sleep() checks for might_fault() when atomic Message-ID: <20141126151729.GB9612@redhat.com> References: <1416915806-24757-1-git-send-email-dahi@linux.vnet.ibm.com> <20141126070258.GA25523@redhat.com> <20141126110504.511b733a@thinkpad-w530> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20141126110504.511b733a@thinkpad-w530> Cc: linux-arch@vger.kernel.org, heiko.carstens@de.ibm.com, linux-kernel@vger.kernel.org, borntraeger@de.ibm.com, paulus@samba.org, schwidefsky@de.ibm.com, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, mingo@kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, Nov 26, 2014 at 11:05:04AM +0100, David Hildenbrand wrote: > > What's the path you are trying to debug? > > Well, we had a problem where we held a spin_lock and called > copy_(from|to)_user(). We experienced very random deadlocks that took some guy > almost a week to debug. The simple might_sleep() check would have showed this > error immediately. This must have been a very old kernel. A modern kernel will return an error from copy_to_user. Which is really the point of the patch you are trying to revert.