Patchset for kernel 3.10 (fixing lockup in printk)

index 1c0577383af5..c3ad3b834f68 100644
@@ -103,6 +103,7 @@ enum {
 };
 static long printk_handover_state;
 
+#ifdef CONFIG_PRINTK_OFFLOAD
 /*
  * Number of kernel threads for offloading printing. We need at least two so
  * that they can hand over printing from one to another one and thus switch

@@ -116,6 +117,7 @@ static DEFINE_MUTEX(printk_kthread_mutex);
 
 /* Wait queue printing kthreads sleep on when idle */
 static DECLARE_WAIT_QUEUE_HEAD(print_queue); 
+#endif	/* CONFIG_PRINTK_OFFLOAD */
 
 #ifdef CONFIG_LOCKDEP
 static struct lockdep_map console_lock_dep_map = {

@@ -284,6 +286,7 @@ static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
 static char *log_buf = __log_buf;
 static u32 log_buf_len = __LOG_BUF_LEN;
 
+#ifdef CONFIG_PRINTK_OFFLOAD
 static int offload_chars_set(const char *val, const struct kernel_param *kp);
 static struct kernel_param_ops offload_chars_ops = {
 	.set = offload_chars_set,

@@ -302,6 +305,7 @@ module_param_cb(offload_chars, &offload_chars_ops, &printk_offload_chars,
 		   S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(offload_chars, "offload printing to console to a different"
 	" cpu after this number of characters");
+#endif
 
 /* human readable text of the record */
 static char *log_text(const struct printk_log *msg)

@@ -2021,6 +2025,7 @@ int console_trylock(void)
 }
 EXPORT_SYMBOL(console_trylock);
 
+#ifdef CONFIG_PRINTK_OFFLOAD
 /*
  * This is a version of console_lock() which spins to acquire console_sem.
  * It is only for use by threads that take care of flushing printk buffer so

@@ -2052,6 +2057,7 @@ static int console_lock_try_spin(void)
 	mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);
 	return 1;
 }
+#endif
 
 int is_console_locked(void)
 {

@@ -2087,6 +2093,7 @@ out:
 	raw_spin_unlock_irqrestore(&logbuf_lock, flags);
 }
 
+#ifdef CONFIG_PRINTK_OFFLOAD
 /*
  * Returns true iff there is other cpu waiting to take over printing. This
  * function also takes are of setting PRINTK_HANDOVER_B if we want to hand over

@@ -2113,6 +2120,7 @@ static bool cpu_stop_printing(int printed_chars)
 	}
 	return false;
 }
+#endif
 
 /**
  * console_unlock - unlock the console system

@@ -2155,10 +2163,12 @@ again:
 		size_t len;
 		int level;
 
+#ifdef CONFIG_PRINTK_OFFLOAD
 		if (cpu_stop_printing(printed_chars)) {
 			hand_over = true;
 			break;
 		}
+#endif
 
 		raw_spin_lock_irqsave(&logbuf_lock, flags);
 		if (seen_seq != log_next_seq) {

@@ -2576,6 +2586,7 @@ int unregister_console(struct console *console)
 }
 EXPORT_SYMBOL(unregister_console);
 
+#ifdef CONFIG_PRINTK_OFFLOAD
 /* Kthread which takes over printing from a CPU which asks for help */
 static int printing_task(void *arg)
 {

@@ -2638,6 +2649,7 @@ static int offload_chars_set(const char *val, const struct kernel_param *kp)
 	mutex_unlock(&printk_kthread_mutex);
 	return 0;
 }
+#endif	/* CONFIG_PRINTK_OFFLOAD */
 
 static int __init printk_late_init(void)
 {

@@ -2650,9 +2662,11 @@ static int __init printk_late_init(void)
 	}
 	hotcpu_notifier(console_cpu_notify, 0);
 
+#ifdef CONFIG_PRINTK_OFFLOAD
 	mutex_lock(&printk_kthread_mutex);
 	printk_start_offload_kthreads();
 	mutex_unlock(&printk_kthread_mutex);
+#endif
 
 	return 0;
 }

81 lines not on this page · raw message

index 7571a16bd653..c61c169f85b3 100644
@@ -150,6 +150,7 @@ extern int console_trylock(void);
 extern void console_unlock(void);
 extern void console_conditional_schedule(void);
 extern void console_unblank(void);
+extern void console_flush(void);
 extern struct tty_driver *console_device(int *);
 extern void console_stop(struct console *);
 extern void console_start(struct console *);

index 8d981b2b5bb1..1c0577383af5 100644
@@ -2306,6 +2306,28 @@ struct tty_driver *console_device(int *index)
 }
 
 /*
+ * Wait until all messages accumulated in the printk buffer are printed to
+ * console. Note that as soon as this function returns, new messages may be
+ * added to the printk buffer by other CPUs.
+ */
+void console_flush(void)
+{
+	bool retry;
+	unsigned long flags;
+
+	while (1) {
+		raw_spin_lock_irqsave(&logbuf_lock, flags);
+		retry = console_seq != log_next_seq;
+		raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+		if (!retry || console_suspended)
+			break;
+		/* Cycle console_sem to wait for outstanding printing */
+		console_lock();
+		console_unlock();
+	}
+}
+
+/*
  * Prevent further output on the passed console device so that (for example)
  * serial drivers can disable console output before suspending a port, and can
  * re-enable output afterwards.

index 84571e09c907..14ac740e0c7f 100644
@@ -21,5 +21,6 @@
 #include <linux/smpboot.h>
 #include <linux/atomic.h>
+#include <linux/console.h>
 
 /*
  * Structure to determine completion condition and record errors.  May

@@ -574,6 +575,14 @@ int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
 		return ret;
 	}
 
+	/*
+	 * If there are lots of outstanding messages, printing them can take a
+	 * long time and all cpus would be spinning waiting for the printing to
+	 * finish thus triggering NMI watchdog, RCU lockups etc. Wait for the
+	 * printing here to avoid these.
+	 */
+	console_flush();
+
 	/* Set the initial state and stop all online cpus. */
 	set_state(&msdata, MULTI_STOP_PREPARE);
 	return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);

101 lines not on this page · raw message

index 4dae9cbe9259..bd7ee2a9f960 100644
@@ -206,8 +206,7 @@ struct printk_log {
 };
 
 /*
- * The logbuf_lock protects kmsg buffer, indices, counters. It is also
- * used in interesting ways to provide interlocking in console_unlock();
+ * The logbuf_lock protects kmsg buffer, indices, counters.
  */
 static DEFINE_RAW_SPINLOCK(logbuf_lock);
 

302 lines not on this page · raw message

index 7a8ffd89875c..56649edfae9c 100644
@@ -1314,10 +1314,9 @@ static int have_callable_console(void)
 /*
  * Can we actually use the console at this time on this cpu?
  *
- * Console drivers may assume that per-cpu resources have
- * been allocated. So unless they're explicitly marked as
- * being able to cope (CON_ANYTIME) don't call them until
- * this CPU is officially up.
+ * Console drivers may assume that per-cpu resources have been allocated. So
+ * unless they're explicitly marked as being able to cope (CON_ANYTIME) don't
+ * call them until this CPU is officially up.
  */
 static inline int can_use_console(unsigned int cpu)
 {

@@ -1330,8 +1329,10 @@ static inline int can_use_console(unsigned int cpu)
  * console_lock held, and 'console_locked' set) if it
  * is successful, false otherwise.
  */
-static int console_trylock_for_printk(unsigned int cpu)
+static int console_trylock_for_printk(void)
 {
+	unsigned int cpu = smp_processor_id();
+
 	if (!console_trylock())
 		return 0;
 	/*

@@ -1501,7 +1502,8 @@ asmlinkage int vprintk_emit(int facility, int level,
 		 */
 		if (!oops_in_progress && !lockdep_recursing(current)) {
 			recursion_bug = 1;
-			goto out_restore_irqs;
+			local_irq_restore(flags);
+			return 0;
 		}
 		zap_locks();
 	}

@@ -1597,17 +1599,22 @@ asmlinkage int vprintk_emit(int facility, int level,
 
 	logbuf_cpu = UINT_MAX;
 	raw_spin_unlock(&logbuf_lock);
+	lockdep_on();
+	local_irq_restore(flags);
+
+	/*
+	 * Disable preemption to avoid being preempted while holding
+	 * console_sem which would prevent anyone from printing to console
+	 */
+	preempt_disable();
 	/*
 	 * Try to acquire and then immediately release the console semaphore.
 	 * The release will print out buffers and wake up /dev/kmsg and syslog()
 	 * users.
 	 */
-	if (console_trylock_for_printk(this_cpu))
+	if (console_trylock_for_printk())
 		console_unlock();
-
-	lockdep_on();
-out_restore_irqs:
-	local_irq_restore(flags);
+	preempt_enable();
 
 	return printed_len;
 }

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