Description of problem:
The megaraid_sas driver uses pci_alloc_consistent to allocate an array of
buffers to copy user arguments into within the ioctl path.

This can fail under heavy load leading to messages like:

megasas: Failed to alloc kernel SGL buffer for IOCTL

Upstream fixed this here:

commit 9f35fa8a14e6216a859e2dfbe50ade497f9603ef
Author: Sumant Patro <sumantp>
Date:   Wed Feb 14 12:55:45 2007 -0800

    [SCSI] megaraid_sas: replace pci_alloc_consitent with dma_alloc_coherent in
ioctl path
    
    Replaced pci_alloc_consistent with dma_alloc_coherent from the ioctl path.
    This is to avoid situations where ioctl fails for lack of memory
    (when system under heavy stress).
    
    Signed-off-by: Sumant Patro <sumant.patro>
    Signed-off-by: James Bottomley <James.Bottomley>


Appearing in dmesg.

Version-Release number of selected component (if applicable):
kernel-2.6.9-55.EL

How reproducible:
Moderate; problem was observed during pre-production stress testing of boxes
using megaraid_sas as the primary storage.

Steps to Reproduce:
1. Configure a system with megaraid_sas providing storage
2. Create memory pressure on the system while something is attempting ioctl
commands on the megaraid
  
Actual results:
Appearance of:
"megasas: Failed to alloc kernel SGL buffer for IOCTL"

in dmesg.

Expected results:
Megaraid_sas ioctls succeed.