Re: [PATCH v3 3/4] uaccess: Check no rescheduling function is called in unsafe region

On Mon, Feb 11, 2019 at 02:45:27PM +0100, Ingo Molnar wrote:

quoted

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a674c7db..b1bb7e9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c

@@ -3289,6 +3289,14 @@ static inline void schedule_debug(struct task_struct *prev)
 		__schedule_bug(prev);
 		preempt_count_set(PREEMPT_DISABLED);
 	}
+
+	if (IS_ENABLED(CONFIG_DEBUG_UACCESS_SLEEP) &&
+	    unlikely(unsafe_user_region_active())) {
+		printk(KERN_ERR "BUG: scheduling while user_access enabled: %s/%d/0x%08x\n",
+		       prev->comm, prev->pid, preempt_count());
+		dump_stack();
+	}
+
 	rcu_sleep_check();

 	profile_hit(SCHED_PROFILING, __builtin_return_address(0));

@@ -6151,6 +6159,20 @@ void ___might_sleep(const char *file, int line, int preempt_offset)
 EXPORT_SYMBOL(___might_sleep);
 #endif

+#ifdef CONFIG_DEBUG_UACCESS_SLEEP
+void __might_resched(const char *file, int line)
+{
+	if (!unsafe_user_region_active())
+		return;

Could you please more clearly explain why you want/need an exception from 
the __might_resched() debug warning?

In specific; how is the addition in schedule_debug() not triggering on
PREEMPT=y kernels?

If code is preemptible, you can (get) schedule(d). If it is not
preemptible; you do not need these additional tests.

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