From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757339Ab3FTVQr (ORCPT ); Thu, 20 Jun 2013 17:16:47 -0400 Received: from mx1.redhat.com ([209.132.183.28]:28827 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755518Ab3FTVQp (ORCPT ); Thu, 20 Jun 2013 17:16:45 -0400 Date: Thu, 20 Jun 2013 18:05:56 -0300 From: Marcelo Tosatti To: Dave Airlie Cc: linux-kernel@vger.kernel.org, Gleb Natapov , Paolo Bonzini Subject: [PATCH] vgacon.c: add cond reschedule points in vgacon_do_font_op Message-ID: <20130620210556.GA13479@amt.cnet> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Booting a 64-vcpu KVM guest, with CONFIG_PREEMPT_VOLUNTARY, can result in a soft lockup: BUG: soft lockup - CPU#41 stuck for 67s! [setfont:1505] RIP: 0010:[] [] vgacon_do_font_op.clone.0+0x1ba/0x550 This is due to the 8192 (cmapsz) IO operations taking longer than expected due to lock contention in QEMU. Add conditional resched points in between writes allowing other tasks to execute. Signed-off-by: Marcelo Tosatti diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c index 5855d17..0dd6d96 100644 --- a/drivers/video/console/vgacon.c +++ b/drivers/video/console/vgacon.c @@ -1124,11 +1124,15 @@ static int vgacon_do_font_op(struct vgastate *state,char *arg,int set,int ch512) if (arg) { if (set) - for (i = 0; i < cmapsz; i++) + for (i = 0; i < cmapsz; i++) { vga_writeb(arg[i], charmap + i); + cond_resched(); + } else - for (i = 0; i < cmapsz; i++) + for (i = 0; i < cmapsz; i++) { arg[i] = vga_readb(charmap + i); + cond_resched(); + } /* * In 512-character mode, the character map is not contiguous if @@ -1139,11 +1143,15 @@ static int vgacon_do_font_op(struct vgastate *state,char *arg,int set,int ch512) charmap += 2 * cmapsz; arg += cmapsz; if (set) - for (i = 0; i < cmapsz; i++) + for (i = 0; i < cmapsz; i++) { vga_writeb(arg[i], charmap + i); + cond_resched(); + } else - for (i = 0; i < cmapsz; i++) + for (i = 0; i < cmapsz; i++) { arg[i] = vga_readb(charmap + i); + cond_resched(); + } } }