[PATCH] random: Fix the issue of '_might_sleep' function running in an atomic contex

[Guoyong Wang]

'input_handle_event' runs in an atomic context
(spinlock). In rare instances, it may call
the '_might_sleep' function, which could trigger
a kernel exception.

Backtrace:
  [<ffffffd613025ba0>] die+0xa8/0x2fc
  [<ffffffd613027428>] bug_handler+0x44/0xec
  [<ffffffd613016964>] brk_handler+0x90/0x144
  [<ffffffd613041e58>] do_debug_exception+0xa0/0x148
  [<ffffffd61400c208>] el1_dbg+0x60/0x7c
  [<ffffffd61400c000>] el1h_64_sync_handler+0x38/0x90
  [<ffffffd613011294>] el1h_64_sync+0x64/0x6c
  [<ffffffd613102d88>] __might_resched+0x1fc/0x2e8
  [<ffffffd613102b54>] __might_sleep+0x44/0x7c
  [<ffffffd6130b6eac>] cpus_read_lock+0x1c/0xec
  [<ffffffd6132c2820>] static_key_enable+0x14/0x38
  [<ffffffd61400ac08>] crng_set_ready+0x14/0x28
  [<ffffffd6130df4dc>] execute_in_process_context+0xb8/0xf8
  [<ffffffd61400ab30>] _credit_init_bits+0x118/0x1dc
  [<ffffffd6138580c8>] add_timer_randomness+0x264/0x270
  [<ffffffd613857e54>] add_input_randomness+0x38/0x48
  [<ffffffd613a80f94>] input_handle_event+0x2b8/0x490
  [<ffffffd613a81310>] input_event+0x6c/0x98

Signed-off-by: Guoyong Wang <guoyong.wang at mediatek.com>
---
 drivers/char/random.c     |  2 +-
 include/linux/workqueue.h |  1 +
 kernel/workqueue.c        | 26 ++++++++++++++++++++++++++
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 456be28ba67c..00be9426a6fc 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -719,7 +719,7 @@ static void __cold _credit_init_bits(size_t bits)
 	if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) {
 		crng_reseed(NULL); /* Sets crng_init to CRNG_READY under base_crng.lock. */
 		if (static_key_initialized)
-			execute_in_process_context(crng_set_ready, &set_ready);
+			execute_in_non_atomic_context(crng_set_ready, &set_ready);
 		atomic_notifier_call_chain(&random_ready_notifier, 0, NULL);
 		wake_up_interruptible(&crng_init_wait);
 		kill_fasync(&fasync, SIGIO, POLL_IN);
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 158784dd189a..eb17c62d23aa 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -550,6 +550,7 @@ extern void drain_workqueue(struct workqueue_struct *wq);
 extern int schedule_on_each_cpu(work_func_t func);
 
 int execute_in_process_context(work_func_t fn, struct execute_work *);
+int execute_in_non_atomic_context(work_func_t fn, struct execute_work *ew);
 
 extern bool flush_work(struct work_struct *work);
 extern bool cancel_work(struct work_struct *work);
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index bf2bdac46843..8f212346da7a 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4449,6 +4449,32 @@ int execute_in_process_context(work_func_t fn, struct execute_work *ew)
 }
 EXPORT_SYMBOL_GPL(execute_in_process_context);
 
+/**
+ * execute_in_non_atomic_context - reliably execute the routine with user context
+ * @fn:		the function to execute
+ * @ew:		guaranteed storage for the execute work structure (must
+ *		be available when the work executes)
+ *
+ * Schedules the function for delayed execution if atomic context is available,
+ * otherwise executes the function immediately .
+ *
+ * Return:	0 - function was executed
+ *		1 - function was scheduled for execution
+ */
+int execute_in_non_atomic_context(work_func_t fn, struct execute_work *ew)
+{
+	if (!in_atomic()) {
+		fn(&ew->work);
+		return 0;
+	}
+
+	INIT_WORK(&ew->work, fn);
+	schedule_work(&ew->work);
+
+	return 1;
+}
+EXPORT_SYMBOL_GPL(execute_in_non_atomic_context);
+
 /**
  * free_workqueue_attrs - free a workqueue_attrs
  * @attrs: workqueue_attrs to free
-- 
2.18.0