[3.19.y-ckt stable] Patch "drivers/base: cacheinfo: handle absence of caches" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    drivers/base: cacheinfo: handle absence of caches

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt3.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From b8cc91d0a874cf39cc858054b711a0e989b200bf Mon Sep 17 00:00:00 2001
From: Sudeep Holla <sudeep.holla at arm.com>
Date: Wed, 27 May 2015 11:26:13 +0100
Subject: drivers/base: cacheinfo: handle absence of caches

commit 3370e13aa463adb84488ebf0e599e3dc0024315b upstream.

On some simulators like GEM5, caches may not be simulated. In those
cases, the cache levels and leaves will be zero and will result in
following exception:

Unable to handle kernel NULL pointer dereference at virtual address 0040
pgd = ffffffc0008fa000
[00000040] *pgd=00000009f6807003, *pud=00000009f6807003,
	   *pmd=00000009f6808003, *pte=006000002c010707
Internal error: Oops: 96000005 [#1] PREEMPT SMP
Modules linked in:
CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.1.0-rc5 #198
task: ffffffc9768a0000 ti: ffffffc9768a8000 task.ti: ffffffc9768a8000
PC is at detect_cache_attributes+0x98/0x2c8
LR is at detect_cache_attributes+0x88/0x2c8

kcalloc(0) returns a special value ZERO_SIZE_PTR which is non-NULL value
but results in fault only on any attempt to dereferencing it. So
checking for the non-NULL pointer will not suffice.

This patch checks for non-zero cache leaf nodes and returns error if
there are no cache leaves in detect_cache_attributes.

Cc: Will Deacon <will.deacon at arm.com>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Reported-by: William Wang <william.wang at arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla at arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/base/cacheinfo.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
index 9c2ba1c..df0c66c 100644
--- a/drivers/base/cacheinfo.c
+++ b/drivers/base/cacheinfo.c
@@ -179,7 +179,7 @@ static int detect_cache_attributes(unsigned int cpu)
 {
 	int ret;

-	if (init_cache_level(cpu))
+	if (init_cache_level(cpu) || !cache_leaves(cpu))
 		return -ENOENT;

 	per_cpu_cacheinfo(cpu) = kcalloc(cache_leaves(cpu),
--
1.9.1