From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752840AbcHNSRt (ORCPT ); Sun, 14 Aug 2016 14:17:49 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:54887 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750975AbcHNR5p (ORCPT ); Sun, 14 Aug 2016 13:57:45 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Raghava Aditya Renukunta" , "Martin K. Petersen" , "Johannes Thumshirn" Date: Sat, 13 Aug 2016 18:42:51 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 032/305] aacraid: Relinquish CPU during timeout wait In-Reply-To: X-SA-Exim-Connect-IP: 92.40.249.202 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.37-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Raghava Aditya Renukunta commit 07beca2be24cc710461c0b131832524c9ee08910 upstream. aac_fib_send has a special function case for initial commands during driver initialization using wait < 0(pseudo sync mode). In this case, the command does not sleep but rather spins checking for timeout.This loop is calls cpu_relax() in an attempt to allow other processes/threads to use the CPU, but this function does not relinquish the CPU and so the command will hog the processor. This was observed in a KDUMP "crashkernel" and that prevented the "command thread" (which is responsible for completing the command from being timed out) from starting because it could not get the CPU. Fixed by replacing "cpu_relax()" call with "schedule()" Signed-off-by: Raghava Aditya Renukunta Reviewed-by: Johannes Thumshirn Signed-off-by: Martin K. Petersen Signed-off-by: Ben Hutchings --- drivers/scsi/aacraid/commsup.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- a/drivers/scsi/aacraid/commsup.c +++ b/drivers/scsi/aacraid/commsup.c @@ -590,10 +590,10 @@ int aac_fib_send(u16 command, struct fib } return -EFAULT; } - /* We used to udelay() here but that absorbed - * a CPU when a timeout occured. Not very - * useful. */ - cpu_relax(); + /* + * Allow other processes / CPUS to use core + */ + schedule(); } } else if (down_interruptible(&fibptr->event_wait)) { /* Do nothing ... satisfy