Merge branch 'rework/kthreads' into for-linus

Author: pmladek

drivers/tty/sysrq.c

@@ -578,6 +578,7 @@ void __handle_sysrq(int key, bool check_mask)
 
 	rcu_sysrq_start();
 	rcu_read_lock();
+	printk_prefer_direct_enter();
 	/*
 	 * Raise the apparent loglevel to maximum so that the sysrq header
 	 * is shown to provide the user with positive feedback.  We do not
@@ -619,6 +620,7 @@ void __handle_sysrq(int key, bool check_mask)
 		pr_cont("\n");
 		console_loglevel = orig_log_level;
 	}
+	printk_prefer_direct_exit();
 	rcu_read_unlock();
 	rcu_sysrq_end();
 

include/linux/console.h

@@ -16,6 +16,7 @@
 
 #include <linux/atomic.h>
 #include <linux/types.h>
+#include <linux/mutex.h>
 
 struct vc_data;
 struct console_font_op;
@@ -151,6 +152,24 @@ struct console {
 	int	cflag;
 	uint	ispeed;
 	uint	ospeed;
+	u64	seq;
+	unsigned long dropped;
+	struct task_struct *thread;
+	bool	blocked;
+
+	/*
+	 * The per-console lock is used by printing kthreads to synchronize
+	 * this console with callers of console_lock(). This is necessary in
+	 * order to allow printing kthreads to run in parallel to each other,
+	 * while each safely accessing the @blocked field and synchronizing
+	 * against direct printing via console_lock/console_unlock.
+	 *
+	 * Note: For synchronizing against direct printing via
+	 *       console_trylock/console_unlock, see the static global
+	 *       variable @console_kthreads_active.
+	 */
+	struct mutex lock;
+
 	void	*data;
 	struct	 console *next;
 };

include/linux/printk.h

@@ -170,6 +170,11 @@ extern void __printk_safe_exit(void);
 #define printk_deferred_enter __printk_safe_enter
 #define printk_deferred_exit __printk_safe_exit
 
+extern void printk_prefer_direct_enter(void);
+extern void printk_prefer_direct_exit(void);
+
+extern bool pr_flush(int timeout_ms, bool reset_on_progress);
+
 /*
  * Please don't use printk_ratelimit(), because it shares ratelimiting state
  * with all other unrelated printk_ratelimit() callsites.  Instead use
@@ -220,6 +225,19 @@ static inline void printk_deferred_exit(void)
 {
 }
 
+static inline void printk_prefer_direct_enter(void)
+{
+}
+
+static inline void printk_prefer_direct_exit(void)
+{
+}
+
+static inline bool pr_flush(int timeout_ms, bool reset_on_progress)
+{
+	return true;
+}
+
 static inline int printk_ratelimit(void)
 {
 	return 0;
@@ -277,45 +295,57 @@ static inline void printk_trigger_flush(void)
 #endif
 
 #ifdef CONFIG_SMP
-extern int __printk_cpu_trylock(void);
-extern void __printk_wait_on_cpu_lock(void);
-extern void __printk_cpu_unlock(void);
+extern int __printk_cpu_sync_try_get(void);
+extern void __printk_cpu_sync_wait(void);
+extern void __printk_cpu_sync_put(void);
+
+#else
+
+#define __printk_cpu_sync_try_get() true
+#define __printk_cpu_sync_wait()
+#define __printk_cpu_sync_put()
+#endif /* CONFIG_SMP */
 
 /**
- * printk_cpu_lock_irqsave() - Acquire the printk cpu-reentrant spinning
- *                             lock and disable interrupts.
+ * printk_cpu_sync_get_irqsave() - Disable interrupts and acquire the printk
+ *                                 cpu-reentrant spinning lock.
  * @flags: Stack-allocated storage for saving local interrupt state,
- *         to be passed to printk_cpu_unlock_irqrestore().
+ *         to be passed to printk_cpu_sync_put_irqrestore().
  *
  * If the lock is owned by another CPU, spin until it becomes available.
  * Interrupts are restored while spinning.
+ *
+ * CAUTION: This function must be used carefully. It does not behave like a
+ * typical lock. Here are important things to watch out for...
+ *
+ *     * This function is reentrant on the same CPU. Therefore the calling
+ *       code must not assume exclusive access to data if code accessing the
+ *       data can run reentrant or within NMI context on the same CPU.
+ *
+ *     * If there exists usage of this function from NMI context, it becomes
+ *       unsafe to perform any type of locking or spinning to wait for other
+ *       CPUs after calling this function from any context. This includes
+ *       using spinlocks or any other busy-waiting synchronization methods.
  */
-#define printk_cpu_lock_irqsave(flags)		\
-	for (;;) {				\
-		local_irq_save(flags);		\
-		if (__printk_cpu_trylock())	\
-			break;			\
-		local_irq_restore(flags);	\
-		__printk_wait_on_cpu_lock();	\
+#define printk_cpu_sync_get_irqsave(flags)		\
+	for (;;) {					\
+		local_irq_save(flags);			\
+		if (__printk_cpu_sync_try_get())	\
+			break;				\
+		local_irq_restore(flags);		\
+		__printk_cpu_sync_wait();		\
 	}
 
 /**
- * printk_cpu_unlock_irqrestore() - Release the printk cpu-reentrant spinning
- *                                  lock and restore interrupts.
- * @flags: Caller's saved interrupt state, from printk_cpu_lock_irqsave().
+ * printk_cpu_sync_put_irqrestore() - Release the printk cpu-reentrant spinning
+ *                                    lock and restore interrupts.
+ * @flags: Caller's saved interrupt state, from printk_cpu_sync_get_irqsave().
  */
-#define printk_cpu_unlock_irqrestore(flags)	\
+#define printk_cpu_sync_put_irqrestore(flags)	\
 	do {					\
-		__printk_cpu_unlock();		\
+		__printk_cpu_sync_put();	\
 		local_irq_restore(flags);	\
-	} while (0)				\
-
-#else
-
-#define printk_cpu_lock_irqsave(flags) ((void)flags)
-#define printk_cpu_unlock_irqrestore(flags) ((void)flags)
-
-#endif /* CONFIG_SMP */
+	} while (0)
 
 extern int kptr_restrict;
 

kernel/hung_task.c

@@ -127,6 +127,8 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
 	 * complain:
 	 */
 	if (sysctl_hung_task_warnings) {
+		printk_prefer_direct_enter();
+
 		if (sysctl_hung_task_warnings > 0)
 			sysctl_hung_task_warnings--;
 		pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
@@ -142,6 +144,8 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
 
 		if (sysctl_hung_task_all_cpu_backtrace)
 			hung_task_show_all_bt = true;
+
+		printk_prefer_direct_exit();
 	}
 
 	touch_nmi_watchdog();
@@ -204,12 +208,17 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
 	}
  unlock:
 	rcu_read_unlock();
-	if (hung_task_show_lock)
+	if (hung_task_show_lock) {
+		printk_prefer_direct_enter();
 		debug_show_all_locks();
+		printk_prefer_direct_exit();
+	}
 
 	if (hung_task_show_all_bt) {
 		hung_task_show_all_bt = false;
+		printk_prefer_direct_enter();
 		trigger_all_cpu_backtrace();
+		printk_prefer_direct_exit();
 	}
 
 	if (hung_task_call_panic)

kernel/panic.c

@@ -560,6 +560,8 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
 {
 	disable_trace_on_warning();
 
+	printk_prefer_direct_enter();
+
 	if (file)
 		pr_warn("WARNING: CPU: %d PID: %d at %s:%d %pS\n",
 			raw_smp_processor_id(), current->pid, file, line,
@@ -597,6 +599,8 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
 
 	/* Just a warning, don't kill lockdep. */
 	add_taint(taint, LOCKDEP_STILL_OK);
+
+	printk_prefer_direct_exit();
 }
 
 #ifndef __WARN_FLAGS