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

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