Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030290AbVIVT65 (ORCPT ); Thu, 22 Sep 2005 15:58:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030286AbVIVT64 (ORCPT ); Thu, 22 Sep 2005 15:58:56 -0400 Received: from smtp.osdl.org ([65.172.181.4]:32943 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S1030290AbVIVT64 (ORCPT ); Thu, 22 Sep 2005 15:58:56 -0400 Date: Thu, 22 Sep 2005 12:58:01 -0700 From: Andrew Morton To: Blaisorblade Cc: user-mode-linux-devel@lists.sourceforge.net, torvalds@osdl.org, jdike@addtoit.com, linux-kernel@vger.kernel.org Subject: Re: [uml-devel] Re: [PATCH 07/10] uml: avoid fixing faults while atomic Message-Id: <20050922125801.1b7894d2.akpm@osdl.org> In-Reply-To: <200509222137.41412.blaisorblade@yahoo.it> References: <200509211923.21861.blaisorblade@yahoo.it> <200509212222.50653.blaisorblade@yahoo.it> <20050921134724.52603016.akpm@osdl.org> <200509222137.41412.blaisorblade@yahoo.it> X-Mailer: Sylpheed version 1.0.4 (GTK+ 1.2.10; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1882 Lines: 44 Blaisorblade wrote: > > On Wednesday 21 September 2005 22:47, Andrew Morton wrote: > > Blaisorblade wrote: > > > On Wednesday 21 September 2005 21:49, Andrew Morton wrote: > > > > "Paolo 'Blaisorblade' Giarrusso" wrote: > > > > > From: Paolo 'Blaisorblade' Giarrusso > > > > > It has accidental side-effects, > > > > such as making copy_to_user() fail if inside spinlocks when > > > > CONFIG_PREEMPT=y. > > > > Sorry, but should it ever succeed inside spinlocks? I mean, should it > > > ever call down() inside spinlocks? (We never do down_trylock, and ever if > > > we did the x86 trick, that wouldn't make the whole thing safe at all - > > > they still take the spinlock and potentially sleep. And it's legal only > > > if no spinlock is held). > > > Not sure what you're asking here. > > > copy_to/from_user() will fail inside spinlock if CONFIG_PREMPT=y and if the > > copy happens to cause a fault. > > > Otherwise it will succeed inside spinlock, > > and it won't spew a sleeping-while-atomic warning, because that uses > > in_atomic() too. > > > It might deadlock if we schedule away and try to retake > > the same lock. > Exactly - the point is: is it legal to call copy_from_user() while holding a > spinlock (which is my original question)? Or should copy_from_user try to > satisfy the fault, instead of seeing in_atomic() or something similar and > fail? No, it is not legal to call copy_*_user() while holding a spinlock. If CONFIG_PREEMPT=n, do_page_fault() has no way of knowing that the caller holds a spinlock. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/