linux-kernel - [PATCH 3.16 032/305] aacraid: Relinquish CPU during timeout wait

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Message-ID: <lsq.1471110171.311262366@decadent.org.uk>
Date:	Sat, 13 Aug 2016 18:42:51 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Raghava Aditya Renukunta" <RaghavaAditya.Renukunta@...rosemi.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	"Johannes Thumshirn" <jthumshirn@...e.de>
Subject: [PATCH 3.16 032/305] aacraid: Relinquish CPU during timeout wait

3.16.37-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Raghava Aditya Renukunta <RaghavaAditya.Renukunta@...rosemi.com>

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 <RaghavaAditya.Renukunta@...rosemi.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@...e.de>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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