[tip:smp/hotplug] tracing/rb: Init the CPU mask on allocation

[tip-bot for Sebastian Andrzej Siewior]

Commit-ID:  b18cc3de00ec3442cf40ac60787dbe0703b99e24
Gitweb:     http://git.kernel.org/tip/b18cc3de00ec3442cf40ac60787dbe0703b99e24
Author:     Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
AuthorDate: Wed, 7 Dec 2016 14:31:33 +0100
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Wed, 7 Dec 2016 14:36:21 +0100

tracing/rb: Init the CPU mask on allocation

Before commit b32614c03413 ("tracing/rb: Convert to hotplug state machine")
the allocated cpumask was initialized to the mask of online or possible
CPUs. After the CPU hotplug changes the buffer initialization moved to
trace_rb_cpu_prepare() but the cpumask is allocated with alloc_cpumask()
and therefor has random content. As a consequence the cpu buffers are not
initialized and a later access dereferences a NULL pointer.

Use zalloc_cpumask() instead so trace_rb_cpu_prepare() initializes the
buffers properly.

Fixes: b32614c03413 ("tracing/rb: Convert to hotplug state machine")
Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: rostedt@xxxxxxxxxxx
Link: http://lkml.kernel.org/r/20161207133133.hzkcqfllxcdi3joz@xxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

---
 kernel/trace/ring_buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index a7a055f..89a2611a16 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1297,7 +1297,7 @@ struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
 	if (!buffer)
 		return NULL;
 
-	if (!alloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
+	if (!zalloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
 		goto fail_free_buffer;
 
 	nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);