Patch "drivers/base: cacheinfo: handle absence of caches" has been added to the 4.0-stable tree

This is a note to let you know that I've just added the patch titled

drivers/base: cacheinfo: handle absence of caches

to the 4.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drivers-base-cacheinfo-handle-absence-of-caches.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Sudeep Holla <[email protected]>
Date: Wed, 27 May 2015 11:26:13 +0100
Subject: drivers/base: cacheinfo: handle absence of caches

From: Sudeep Holla <[email protected]>

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.

---
 drivers/base/cacheinfo.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -179,7 +179,7 @@ static int detect_cache_attributes(unsig
 {
 	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),

Patches currently in stable-queue which might be from [email protected] are

queue-4.0/drivers-base-cacheinfo-handle-absence-of-caches.patch --
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