Implement probe_kthread_data() which returns kthread_data if
accessible. The function is equivalent to kthread_data() except that
the specified @task may not be a kthread or its vfork_done is already
cleared rendering struct kthread inaccessible. In the former case,
probe_kthread_data() may return any value. In the latter, NULL.
This will be used to safely print debug information without affecting
synchronization in the normal paths. Workqueue debug info printing on
dump_stack() and friends will make use of it.
Signed-off-by: Tejun Heo <t...@kernel.org>
Cc: Oleg Nesterov <o...@redhat.com>
Cc: Andrew Morton <a...@linux-foundation.org>
---
include/linux/kthread.h | 1 +
kernel/kthread.c | 19 +++++++++++++++++++
2 files changed, 20 insertions(+)
diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 8d81664..7dcef33 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -43,6 +43,7 @@ bool kthread_should_stop(void);
bool kthread_should_park(void);
bool kthread_freezable_should_stop(bool *was_frozen);
void *kthread_data(struct task_struct *k);
+void *probe_kthread_data(struct task_struct *k);
int kthread_park(struct task_struct *k);
void kthread_unpark(struct task_struct *k);
void kthread_parkme(void);
diff --git a/kernel/kthread.c b/kernel/kthread.c
index a2fbbb7..31696c8 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -17,6 +17,7 @@
#include <linux/slab.h>
#include <linux/freezer.h>
#include <linux/ptrace.h>
+#include <linux/uaccess.h>
#include <trace/events/sched.h>
static DEFINE_SPINLOCK(kthread_create_lock);
@@ -122,6 +123,24 @@ void *kthread_data(struct task_struct *task)
return to_kthread(task)->data;
}
+/**
+ * probe_kthread_data - speculatively version of kthread_data()
+ * @task: possible kthread task in question
+ *
+ * @task could be a kthread task. Return the data value specified when it
+ * was created if accessible. If @task isn't a kthread task or its data is
+ * inaccessible for any reason, %NULL is returned. This function requires
+ * that @task itself is safe to dereference.
+ */
+void *probe_kthread_data(struct task_struct *task)
+{
+ struct kthread *kthread = to_kthread(task);
+ void *data = NULL;
+
+ probe_kernel_read(&data, &kthread->data, sizeof(data));
+ return data;
+}
+
static void __kthread_parkme(struct kthread *self)
{
__set_current_state(TASK_INTERRUPTIBLE);
--
1.8.1.4
--
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