linux-kernel - [PATCH] drivers/base: cacheinfo: handle absence of caches

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Date:	Wed, 27 May 2015 11:26:13 +0100
From:	Sudeep Holla <sudeep.holla@....com>
To:	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Sudeep Holla <sudeep.holla@....com>,
	William Wang <william.wang@....com>, <stable@...r.kernel.org>,
	Will Deacon <will.deacon@....com>
Subject: [PATCH] drivers/base: cacheinfo: handle absence of caches

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: <stable@...r.kernel.org> # 3.19.x
Cc: Will Deacon <will.deacon@....com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Reported-by: William Wang <william.wang@....com>
Signed-off-by: Sudeep Holla <sudeep.holla@....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 9c2ba1c97c42..df0c66cb7ad3 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

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