Merge branch 'rework/printk_safe-removal' into for-linus

1 files changed, 162 insertions, 106 deletions

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 776e3565f013..825277e1e742 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -351,7 +351,7 @@ static int console_msg_format = MSG_FORMAT_DEFAULT;
  */
 
 /* syslog_lock protects syslog_* variables and write access to clear_seq. */
-static DEFINE_RAW_SPINLOCK(syslog_lock);
+static DEFINE_MUTEX(syslog_lock);
 
 #ifdef CONFIG_PRINTK
 DECLARE_WAIT_QUEUE_HEAD(log_wait);
@@ -727,27 +727,22 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 	if (ret)
 		return ret;
 
-	printk_safe_enter_irq();
 	if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
 		if (file->f_flags & O_NONBLOCK) {
 			ret = -EAGAIN;
-			printk_safe_exit_irq();
 			goto out;
 		}
 
-		printk_safe_exit_irq();
 		ret = wait_event_interruptible(log_wait,
 				prb_read_valid(prb, atomic64_read(&user->seq), r));
 		if (ret)
 			goto out;
-		printk_safe_enter_irq();
 	}
 
 	if (r->info->seq != atomic64_read(&user->seq)) {
 		/* our last seen message is gone, return error and reset */
 		atomic64_set(&user->seq, r->info->seq);
 		ret = -EPIPE;
-		printk_safe_exit_irq();
 		goto out;
 	}
 
@@ -757,7 +752,6 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 				  &r->info->dev_info);
 
 	atomic64_set(&user->seq, r->info->seq + 1);
-	printk_safe_exit_irq();
 
 	if (len > count) {
 		ret = -EINVAL;
@@ -792,7 +786,6 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
 	if (offset)
 		return -ESPIPE;
 
-	printk_safe_enter_irq();
 	switch (whence) {
 	case SEEK_SET:
 		/* the first record */
@@ -813,7 +806,6 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
 	default:
 		ret = -EINVAL;
 	}
-	printk_safe_exit_irq();
 	return ret;
 }
 
@@ -828,7 +820,6 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
 
 	poll_wait(file, &log_wait, wait);
 
-	printk_safe_enter_irq();
 	if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {
 		/* return error when data has vanished underneath us */
 		if (info.seq != atomic64_read(&user->seq))
@@ -836,7 +827,6 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
 		else
 			ret = EPOLLIN|EPOLLRDNORM;
 	}
-	printk_safe_exit_irq();
 
 	return ret;
 }
@@ -869,9 +859,7 @@ static int devkmsg_open(struct inode *inode, struct file *file)
 	prb_rec_init_rd(&user->record, &user->info,
 			&user->text_buf[0], sizeof(user->text_buf));
 
-	printk_safe_enter_irq();
 	atomic64_set(&user->seq, prb_first_valid_seq(prb));
-	printk_safe_exit_irq();
 
 	file->private_data = user;
 	return 0;
@@ -1037,9 +1025,6 @@ static inline void log_buf_add_cpu(void) {}
 
 static void __init set_percpu_data_ready(void)
 {
-	printk_safe_init();
-	/* Make sure we set this flag only after printk_safe() init is done */
-	barrier();
 	__printk_percpu_data_ready = true;
 }
 
@@ -1077,6 +1062,7 @@ void __init setup_log_buf(int early)
 	struct prb_desc *new_descs;
 	struct printk_info info;
 	struct printk_record r;
+	unsigned int text_size;
 	size_t new_descs_size;
 	size_t new_infos_size;
 	unsigned long flags;
@@ -1137,24 +1123,37 @@ void __init setup_log_buf(int early)
 		 new_descs, ilog2(new_descs_count),
 		 new_infos);
 
-	printk_safe_enter_irqsave(flags);
+	local_irq_save(flags);
 
 	log_buf_len = new_log_buf_len;
 	log_buf = new_log_buf;
 	new_log_buf_len = 0;
 
 	free = __LOG_BUF_LEN;
-	prb_for_each_record(0, &printk_rb_static, seq, &r)
-		free -= add_to_rb(&printk_rb_dynamic, &r);
+	prb_for_each_record(0, &printk_rb_static, seq, &r) {
+		text_size = add_to_rb(&printk_rb_dynamic, &r);
+		if (text_size > free)
+			free = 0;
+		else
+			free -= text_size;
+	}
 
-	/*
-	 * This is early enough that everything is still running on the
-	 * boot CPU and interrupts are disabled. So no new messages will
-	 * appear during the transition to the dynamic buffer.
-	 */
 	prb = &printk_rb_dynamic;
 
-	printk_safe_exit_irqrestore(flags);
+	local_irq_restore(flags);
+
+	/*
+	 * Copy any remaining messages that might have appeared from
+	 * NMI context after copying but before switching to the
+	 * dynamic buffer.
+	 */
+	prb_for_each_record(seq, &printk_rb_static, seq, &r) {
+		text_size = add_to_rb(&printk_rb_dynamic, &r);
+		if (text_size > free)
+			free = 0;
+		else
+			free -= text_size;
+	}
 
 	if (seq != prb_next_seq(&printk_rb_static)) {
 		pr_err("dropped %llu messages\n",
@@ -1476,12 +1475,14 @@ static u64 find_first_fitting_seq(u64 start_seq, u64 max_seq, size_t size,
 	return seq;
 }
 
+/* The caller is responsible for making sure @size is greater than 0. */
 static int syslog_print(char __user *buf, int size)
 {
 	struct printk_info info;
 	struct printk_record r;
 	char *text;
 	int len = 0;
+	u64 seq;
 
 	text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
 	if (!text)
@@ -1489,17 +1490,35 @@ static int syslog_print(char __user *buf, int size)
 
 	prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
 
-	while (size > 0) {
+	mutex_lock(&syslog_lock);
+
+	/*
+	 * Wait for the @syslog_seq record to be available. @syslog_seq may
+	 * change while waiting.
+	 */
+	do {
+		seq = syslog_seq;
+
+		mutex_unlock(&syslog_lock);
+		len = wait_event_interruptible(log_wait, prb_read_valid(prb, seq, NULL));
+		mutex_lock(&syslog_lock);
+
+		if (len)
+			goto out;
+	} while (syslog_seq != seq);
+
+	/*
+	 * Copy records that fit into the buffer. The above cycle makes sure
+	 * that the first record is always available.
+	 */
+	do {
 		size_t n;
 		size_t skip;
+		int err;
 
-		printk_safe_enter_irq();
-		raw_spin_lock(&syslog_lock);
-		if (!prb_read_valid(prb, syslog_seq, &r)) {
-			raw_spin_unlock(&syslog_lock);
-			printk_safe_exit_irq();
+		if (!prb_read_valid(prb, syslog_seq, &r))
 			break;
-		}
+
 		if (r.info->seq != syslog_seq) {
 			/* message is gone, move to next valid one */
 			syslog_seq = r.info->seq;
@@ -1526,13 +1545,15 @@ static int syslog_print(char __user *buf, int size)
 			syslog_partial += n;
 		} else
 			n = 0;
-		raw_spin_unlock(&syslog_lock);
-		printk_safe_exit_irq();
 
 		if (!n)
 			break;
 
-		if (copy_to_user(buf, text + skip, n)) {
+		mutex_unlock(&syslog_lock);
+		err = copy_to_user(buf, text + skip, n);
+		mutex_lock(&syslog_lock);
+
+		if (err) {
 			if (!len)
 				len = -EFAULT;
 			break;
@@ -1541,8 +1562,9 @@ static int syslog_print(char __user *buf, int size)
 		len += n;
 		size -= n;
 		buf += n;
-	}
-
+	} while (size);
+out:
+	mutex_unlock(&syslog_lock);
 	kfree(text);
 	return len;
 }
@@ -1561,7 +1583,6 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 		return -ENOMEM;
 
 	time = printk_time;
-	printk_safe_enter_irq();
 	/*
 	 * Find first record that fits, including all following records,
 	 * into the user-provided buffer for this dump.
@@ -1582,23 +1603,20 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 			break;
 		}
 
-		printk_safe_exit_irq();
 		if (copy_to_user(buf + len, text, textlen))
 			len = -EFAULT;
 		else
 			len += textlen;
-		printk_safe_enter_irq();
 
 		if (len < 0)
 			break;
 	}
 
 	if (clear) {
-		raw_spin_lock(&syslog_lock);
+		mutex_lock(&syslog_lock);
 		latched_seq_write(&clear_seq, seq);
-		raw_spin_unlock(&syslog_lock);
+		mutex_unlock(&syslog_lock);
 	}
-	printk_safe_exit_irq();
 
 	kfree(text);
 	return len;
@@ -1606,23 +1624,9 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 
 static void syslog_clear(void)
 {
-	printk_safe_enter_irq();
-	raw_spin_lock(&syslog_lock);
+	mutex_lock(&syslog_lock);
 	latched_seq_write(&clear_seq, prb_next_seq(prb));
-	raw_spin_unlock(&syslog_lock);
-	printk_safe_exit_irq();
-}
-
-/* Return a consistent copy of @syslog_seq. */
-static u64 read_syslog_seq_irq(void)
-{
-	u64 seq;
-
-	raw_spin_lock_irq(&syslog_lock);
-	seq = syslog_seq;
-	raw_spin_unlock_irq(&syslog_lock);
-
-	return seq;
+	mutex_unlock(&syslog_lock);
 }
 
 int do_syslog(int type, char __user *buf, int len, int source)
@@ -1648,11 +1652,6 @@ int do_syslog(int type, char __user *buf, int len, int source)
 			return 0;
 		if (!access_ok(buf, len))
 			return -EFAULT;
-
-		error = wait_event_interruptible(log_wait,
-				prb_read_valid(prb, read_syslog_seq_irq(), NULL));
-		if (error)
-			return error;
 		error = syslog_print(buf, len);
 		break;
 	/* Read/clear last kernel messages */
@@ -1698,12 +1697,10 @@ int do_syslog(int type, char __user *buf, int len, int source)
 		break;
 	/* Number of chars in the log buffer */
 	case SYSLOG_ACTION_SIZE_UNREAD:
-		printk_safe_enter_irq();
-		raw_spin_lock(&syslog_lock);
+		mutex_lock(&syslog_lock);
 		if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
 			/* No unread messages. */
-			raw_spin_unlock(&syslog_lock);
-			printk_safe_exit_irq();
+			mutex_unlock(&syslog_lock);
 			return 0;
 		}
 		if (info.seq != syslog_seq) {
@@ -1731,8 +1728,7 @@ int do_syslog(int type, char __user *buf, int len, int source)
 			}
 			error -= syslog_partial;
 		}
-		raw_spin_unlock(&syslog_lock);
-		printk_safe_exit_irq();
+		mutex_unlock(&syslog_lock);
 		break;
 	/* Size of the log buffer */
 	case SYSLOG_ACTION_SIZE_BUFFER:
@@ -1935,6 +1931,76 @@ static void call_console_drivers(const char *ext_text, size_t ext_len,
 	}
 }
 
+/*
+ * Recursion is tracked separately on each CPU. If NMIs are supported, an
+ * additional NMI context per CPU is also separately tracked. Until per-CPU
+ * is available, a separate "early tracking" is performed.
+ */
+static DEFINE_PER_CPU(u8, printk_count);
+static u8 printk_count_early;
+#ifdef CONFIG_HAVE_NMI
+static DEFINE_PER_CPU(u8, printk_count_nmi);
+static u8 printk_count_nmi_early;
+#endif
+
+/*
+ * Recursion is limited to keep the output sane. printk() should not require
+ * more than 1 level of recursion (allowing, for example, printk() to trigger
+ * a WARN), but a higher value is used in case some printk-internal errors
+ * exist, such as the ringbuffer validation checks failing.
+ */
+#define PRINTK_MAX_RECURSION 3
+
+/*
+ * Return a pointer to the dedicated counter for the CPU+context of the
+ * caller.
+ */
+static u8 *__printk_recursion_counter(void)
+{
+#ifdef CONFIG_HAVE_NMI
+	if (in_nmi()) {
+		if (printk_percpu_data_ready())
+			return this_cpu_ptr(&printk_count_nmi);
+		return &printk_count_nmi_early;
+	}
+#endif
+	if (printk_percpu_data_ready())
+		return this_cpu_ptr(&printk_count);
+	return &printk_count_early;
+}
+
+/*
+ * Enter recursion tracking. Interrupts are disabled to simplify tracking.
+ * The caller must check the boolean return value to see if the recursion is
+ * allowed. On failure, interrupts are not disabled.
+ *
+ * @recursion_ptr must be a variable of type (u8 *) and is the same variable
+ * that is passed to printk_exit_irqrestore().
+ */
+#define printk_enter_irqsave(recursion_ptr, flags)	\
+({							\
+	bool success = true;				\
+							\
+	typecheck(u8 *, recursion_ptr);			\
+	local_irq_save(flags);				\
+	(recursion_ptr) = __printk_recursion_counter();	\
+	if (*(recursion_ptr) > PRINTK_MAX_RECURSION) {	\
+		local_irq_restore(flags);		\
+		success = false;			\
+	} else {					\
+		(*(recursion_ptr))++;			\
+	}						\
+	success;					\
+})
+
+/* Exit recursion tracking, restoring interrupts. */
+#define printk_exit_irqrestore(recursion_ptr, flags)	\
+	do {						\
+		typecheck(u8 *, recursion_ptr);		\
+		(*(recursion_ptr))--;			\
+		local_irq_restore(flags);		\
+	} while (0)
+
 int printk_delay_msec __read_mostly;
 
 static inline void printk_delay(void)
@@ -2037,11 +2103,14 @@ int vprintk_store(int facility, int level,
 	struct prb_reserved_entry e;
 	enum printk_info_flags flags = 0;
 	struct printk_record r;
+	unsigned long irqflags;
 	u16 trunc_msg_len = 0;
 	char prefix_buf[8];
+	u8 *recursion_ptr;
 	u16 reserve_size;
 	va_list args2;
 	u16 text_len;
+	int ret = 0;
 	u64 ts_nsec;
 
 	/*
@@ -2052,6 +2121,9 @@ int vprintk_store(int facility, int level,
 	 */
 	ts_nsec = local_clock();
 
+	if (!printk_enter_irqsave(recursion_ptr, irqflags))
+		return 0;
+
 	/*
 	 * The sprintf needs to come first since the syslog prefix might be
 	 * passed in as a parameter. An extra byte must be reserved so that
@@ -2089,7 +2161,8 @@ int vprintk_store(int facility, int level,
 				prb_commit(&e);
 			}
 
-			return text_len;
+			ret = text_len;
+			goto out;
 		}
 	}
 
@@ -2105,7 +2178,7 @@ int vprintk_store(int facility, int level,
 
 		prb_rec_init_wr(&r, reserve_size + trunc_msg_len);
 		if (!prb_reserve(&e, prb, &r))
-			return 0;
+			goto out;
 	}
 
 	/* fill message */
@@ -2127,7 +2200,10 @@ int vprintk_store(int facility, int level,
 	else
 		prb_final_commit(&e);
 
-	return (text_len + trunc_msg_len);
+	ret = text_len + trunc_msg_len;
+out:
+	printk_exit_irqrestore(recursion_ptr, irqflags);
+	return ret;
 }
 
 asmlinkage int vprintk_emit(int facility, int level,
@@ -2136,7 +2212,6 @@ asmlinkage int vprintk_emit(int facility, int level,
 {
 	int printed_len;
 	bool in_sched = false;
-	unsigned long flags;
 
 	/* Suppress unimportant messages after panic happens */
 	if (unlikely(suppress_printk))
@@ -2150,9 +2225,7 @@ asmlinkage int vprintk_emit(int facility, int level,
 	boot_delay_msec(level);
 	printk_delay();
 
-	printk_safe_enter_irqsave(flags);
 	printed_len = vprintk_store(facility, level, dev_info, fmt, args);
-	printk_safe_exit_irqrestore(flags);
 
 	/* If called from the scheduler, we can not call up(). */
 	if (!in_sched) {
@@ -2573,9 +2646,9 @@ again:
 
 	for (;;) {
 		size_t ext_len = 0;
+		int handover;
 		size_t len;
 
-		printk_safe_enter_irqsave(flags);
 skip:
 		if (!prb_read_valid(prb, console_seq, &r))
 			break;
@@ -2625,19 +2698,22 @@ skip:
 		 * were to occur on another CPU, it may wait for this one to
 		 * finish. This task can not be preempted if there is a
 		 * waiter waiting to take over.
+		 *
+		 * Interrupts are disabled because the hand over to a waiter
+		 * must not be interrupted until the hand over is completed
+		 * (@console_waiter is cleared).
 		 */
+		printk_safe_enter_irqsave(flags);
 		console_lock_spinning_enable();
 
 		stop_critical_timings();	/* don't trace print latency */
 		call_console_drivers(ext_text, ext_len, text, len);
 		start_critical_timings();
 
-		if (console_lock_spinning_disable_and_check()) {
-			printk_safe_exit_irqrestore(flags);
-			return;
-		}
-
+		handover = console_lock_spinning_disable_and_check();
 		printk_safe_exit_irqrestore(flags);
+		if (handover)
+			return;
 
 		if (do_cond_resched)
 			cond_resched();
@@ -2656,8 +2732,6 @@ skip:
 	 * flush, no worries.
 	 */
 	retry = prb_read_valid(prb, next_seq, NULL);
-	printk_safe_exit_irqrestore(flags);
-
 	if (retry && console_trylock())
 		goto again;
 }
@@ -2719,13 +2793,8 @@ void console_flush_on_panic(enum con_flush_mode mode)
 	console_trylock();
 	console_may_schedule = 0;
 
-	if (mode == CONSOLE_REPLAY_ALL) {
-		unsigned long flags;
-
-		printk_safe_enter_irqsave(flags);
+	if (mode == CONSOLE_REPLAY_ALL)
 		console_seq = prb_first_valid_seq(prb);
-		printk_safe_exit_irqrestore(flags);
-	}
 	console_unlock();
 }
 
@@ -2860,7 +2929,6 @@ static int try_enable_new_console(struct console *newcon, bool user_specified)
  */
 void register_console(struct console *newcon)
 {
-	unsigned long flags;
 	struct console *bcon = NULL;
 	int err;
 
@@ -2965,9 +3033,9 @@ void register_console(struct console *newcon)
 		exclusive_console_stop_seq = console_seq;
 
 		/* Get a consistent copy of @syslog_seq. */
-		raw_spin_lock_irqsave(&syslog_lock, flags);
+		mutex_lock(&syslog_lock);
 		console_seq = syslog_seq;
-		raw_spin_unlock_irqrestore(&syslog_lock, flags);
+		mutex_unlock(&syslog_lock);
 	}
 	console_unlock();
 	console_sysfs_notify();
@@ -3377,14 +3445,12 @@ bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 	struct printk_info info;
 	unsigned int line_count;
 	struct printk_record r;
-	unsigned long flags;
 	size_t l = 0;
 	bool ret = false;
 
 	if (iter->cur_seq < min_seq)
 		iter->cur_seq = min_seq;
 
-	printk_safe_enter_irqsave(flags);
 	prb_rec_init_rd(&r, &info, line, size);
 
 	/* Read text or count text lines? */
@@ -3405,7 +3471,6 @@ bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 	iter->cur_seq = r.info->seq + 1;
 	ret = true;
 out:
-	printk_safe_exit_irqrestore(flags);
 	if (len)
 		*len = l;
 	return ret;
@@ -3437,7 +3502,6 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 	u64 min_seq = latched_seq_read_nolock(&clear_seq);
 	struct printk_info info;
 	struct printk_record r;
-	unsigned long flags;
 	u64 seq;
 	u64 next_seq;
 	size_t len = 0;
@@ -3450,7 +3514,6 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 	if (iter->cur_seq < min_seq)
 		iter->cur_seq = min_seq;
 
-	printk_safe_enter_irqsave(flags);
 	if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
 		if (info.seq != iter->cur_seq) {
 			/* messages are gone, move to first available one */
@@ -3459,10 +3522,8 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 	}
 
 	/* last entry */
-	if (iter->cur_seq >= iter->next_seq) {
-		printk_safe_exit_irqrestore(flags);
+	if (iter->cur_seq >= iter->next_seq)
 		goto out;
-	}
 
 	/*
 	 * Find first record that fits, including all following records,
@@ -3494,7 +3555,6 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 
 	iter->next_seq = next_seq;
 	ret = true;
-	printk_safe_exit_irqrestore(flags);
 out:
 	if (len_out)
 		*len_out = len;
@@ -3512,12 +3572,8 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
  */
 void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
-	unsigned long flags;
-
-	printk_safe_enter_irqsave(flags);
 	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
 	iter->next_seq = prb_next_seq(prb);
-	printk_safe_exit_irqrestore(flags);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);