Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757595Ab2ECRDK (ORCPT ); Thu, 3 May 2012 13:03:10 -0400 Received: from smtp.fullrate.dk ([90.185.1.42]:65035 "EHLO smtp.fullrate.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753044Ab2ECRDI (ORCPT ); Thu, 3 May 2012 13:03:08 -0400 Message-ID: <4FA2BA49.3070902@molgaard.org> Date: Thu, 03 May 2012 19:03:05 +0200 From: =?ISO-8859-1?Q?Sune_M=F8lgaard?= User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/15.0 Firefox/15.0a1 SeaMonkey/2.12a1 MIME-Version: 1.0 To: linux-kernel@vger.kernel.org Subject: Re: Boot failure since 3.3-rc? References: <4F931C6D.8040407@molgaard.org> In-Reply-To: <4F931C6D.8040407@molgaard.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3739 Lines: 91 Incidentally, I had to swap a wifi card, and bisecting now leads to a different bad commit(?) This is what it says is the culprit now (I wonder if I should bisect again, and attempt booting maybe 3 or 4 times each time): f94edacf998516ac9d849f7bc6949a703977a7f3 is the first bad commit commit f94edacf998516ac9d849f7bc6949a703977a7f3 Author: Linus Torvalds Date: Fri Feb 17 21:48:54 2012 -0800 i387: move TS_USEDFPU flag from thread_info to task_struct This moves the bit that indicates whether a thread has ownership of the FPU from the TS_USEDFPU bit in thread_info->status to a word of its own (called 'has_fpu') in task_struct->thread.has_fpu. This fixes two independent bugs at the same time: - changing 'thread_info->status' from the scheduler causes nasty problems for the other users of that variable, since it is defined to be thread-synchronous (that's what the "TS_" part of the naming was supposed to indicate). So perfectly valid code could (and did) do ti->status |= TS_RESTORE_SIGMASK; and the compiler was free to do that as separate load, or and store instructions. Which can cause problems with preemption, since a task switch could happen in between, and change the TS_USEDFPU bit. The change to TS_USEDFPU would be overwritten by the final store. In practice, this seldom happened, though, because the 'status' field was seldom used more than once, so gcc would generally tend to generate code that used a read-modify-write instruction and thus happened to avoid this problem - RMW instructions are naturally low fat and preemption-safe. - On x86-32, the current_thread_info() pointer would, during interrupts and softirqs, point to a *copy* of the real thread_info, because x86-32 uses %esp to calculate the thread_info address, and thus the separate irq (and softirq) stacks would cause these kinds of odd thread_info copy aliases. This is normally not a problem, since interrupts aren't supposed to look at thread information anyway (what thread is running at interrupt time really isn't very well-defined), but it confused the heck out of irq_fpu_usable() and the code that tried to squirrel away the FPU state. (It also caused untold confusion for us poor kernel developers). It also turns out that using 'task_struct' is actually much more natural for most of the call sites that care about the FPU state, since they tend to work with the task struct for other reasons anyway (ie scheduling). And the FPU data that we are going to save/restore is found there too. Thanks to Arjan Van De Ven for pointing us to the %esp issue. Cc: Arjan van de Ven Reported-and-tested-by: Raphael Prevost Acked-and-tested-by: Suresh Siddha Tested-by: Peter Anvin Signed-off-by: Linus Torvalds :040000 040000 19548f49884c9745ecb3970321ff41b244d79b97 ec8b1a02dd7ef354f1be4c68767e4353819dd5fa M arch For obvious reasons, this commit cannot be easily reverted, but help is much appreciated! /sune -- Unix is not an 'a-ha' experience, it is more of a 'holy-shit' experience. - Colin McFadyen -- 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/