From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752638Ab1LLQfz (ORCPT ); Mon, 12 Dec 2011 11:35:55 -0500 Received: from www.linutronix.de ([62.245.132.108]:54161 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750996Ab1LLQfy (ORCPT ); Mon, 12 Dec 2011 11:35:54 -0500 Date: Mon, 12 Dec 2011 17:35:52 +0100 (CET) From: Thomas Gleixner To: Peter Zijlstra cc: Richard Weinberger , linux-kernel@vger.kernel.org Subject: Re: [PATCH -rt] printk: Disable migration instead of preemption In-Reply-To: <1323703531.21400.1.camel@twins> Message-ID: References: <1323696956-11445-1-git-send-email-rw@linutronix.de> <1323703531.21400.1.camel@twins> User-Agent: Alpine 2.02 (LFD 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 12 Dec 2011, Peter Zijlstra wrote: > On Mon, 2011-12-12 at 14:35 +0100, Richard Weinberger wrote: > > There is no need do disable preemption in vprintk(), > > disable_migrate() is sufficient. > > This fixes also a the following bug in -rt: > > > > [ 14.759233] BUG: sleeping function called from invalid context > > at /home/rw/linux-rt/kernel/rtmutex.c:645 > > > --- > > kernel/printk.c | 4 ++-- > > 1 files changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/kernel/printk.c b/kernel/printk.c > > index a50af4e..13d0825 100644 > > --- a/kernel/printk.c > > +++ b/kernel/printk.c > > @@ -898,7 +898,7 @@ asmlinkage int vprintk(const char *fmt, va_list args) > > boot_delay_msec(); > > printk_delay(); > > > > - preempt_disable(); > > + migrate_disable(); > > /* This stops the holder of console_sem just where we want him */ > > raw_local_irq_save(flags); > > this_cpu = smp_processor_id(); > > @@ -1029,7 +1029,7 @@ asmlinkage int vprintk(const char *fmt, va_list args) > > out_restore_irqs: > > raw_local_irq_restore(flags); > > > > - preempt_enable(); > > + migrate_enable(); > > return printed_len; > > } > > EXPORT_SYMBOL(printk); > > One has to wonder why this patch makes any difference what so ever, note > how right after/before the preempt_disable/enable there's a > raw_local_irq_save/restore and last time I checked those really did > disable IRQs, even on -rt. The point is that we drop that lock further down and on RT we also reenable interrupts, so we have to prevent that we get migrated away. Thanks, tglx