Merge tag 'printk-for-5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

Pull printk updates from Petr Mladek:

 - New "no_hash_pointers" kernel parameter causes that %p shows raw
   pointer values instead of hashed ones. It is intended only for
   debugging purposes. Misuse is prevented by a fat warning message that
   is inspired by trace_printk().

 - Prevent a possible deadlock when flushing printk_safe buffers during
   panic().

 - Fix performance regression caused by the lockless printk ringbuffer.
   It was visible with huge log buffer and long messages.

 - Documentation fix-up.

* tag 'printk-for-5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
  lib/vsprintf: no_hash_pointers prints all addresses as unhashed
  kselftest: add support for skipped tests
  lib: use KSTM_MODULE_GLOBALS macro in kselftest drivers
  printk: avoid prb_first_valid_seq() where possible
  printk: fix deadlock when kernel panic
  printk: rectify kernel-doc for prb_rec_init_wr()

3 files changed, 31 insertions, 15 deletions

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 5a95c688621f..575a34b88936 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -735,9 +735,9 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 		logbuf_lock_irq();
 	}
 
-	if (user->seq < prb_first_valid_seq(prb)) {
+	if (r->info->seq != user->seq) {
 		/* our last seen message is gone, return error and reset */
-		user->seq = prb_first_valid_seq(prb);
+		user->seq = r->info->seq;
 		ret = -EPIPE;
 		logbuf_unlock_irq();
 		goto out;
@@ -812,6 +812,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
 static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
 {
 	struct devkmsg_user *user = file->private_data;
+	struct printk_info info;
 	__poll_t ret = 0;
 
 	if (!user)
@@ -820,9 +821,9 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
 	poll_wait(file, &log_wait, wait);
 
 	logbuf_lock_irq();
-	if (prb_read_valid(prb, user->seq, NULL)) {
+	if (prb_read_valid_info(prb, user->seq, &info, NULL)) {
 		/* return error when data has vanished underneath us */
-		if (user->seq < prb_first_valid_seq(prb))
+		if (info.seq != user->seq)
 			ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
 		else
 			ret = EPOLLIN|EPOLLRDNORM;
@@ -1559,6 +1560,7 @@ static void syslog_clear(void)
 
 int do_syslog(int type, char __user *buf, int len, int source)
 {
+	struct printk_info info;
 	bool clear = false;
 	static int saved_console_loglevel = LOGLEVEL_DEFAULT;
 	int error;
@@ -1629,9 +1631,14 @@ int do_syslog(int type, char __user *buf, int len, int source)
 	/* Number of chars in the log buffer */
 	case SYSLOG_ACTION_SIZE_UNREAD:
 		logbuf_lock_irq();
-		if (syslog_seq < prb_first_valid_seq(prb)) {
+		if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
+			/* No unread messages. */
+			logbuf_unlock_irq();
+			return 0;
+		}
+		if (info.seq != syslog_seq) {
 			/* messages are gone, move to first one */
-			syslog_seq = prb_first_valid_seq(prb);
+			syslog_seq = info.seq;
 			syslog_partial = 0;
 		}
 		if (source == SYSLOG_FROM_PROC) {
@@ -1643,7 +1650,6 @@ int do_syslog(int type, char __user *buf, int len, int source)
 			error = prb_next_seq(prb) - syslog_seq;
 		} else {
 			bool time = syslog_partial ? syslog_time : printk_time;
-			struct printk_info info;
 			unsigned int line_count;
 			u64 seq;
 
@@ -3429,9 +3435,11 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 		goto out;
 
 	logbuf_lock_irqsave(flags);
-	if (dumper->cur_seq < prb_first_valid_seq(prb)) {
-		/* messages are gone, move to first available one */
-		dumper->cur_seq = prb_first_valid_seq(prb);
+	if (prb_read_valid_info(prb, dumper->cur_seq, &info, NULL)) {
+		if (info.seq != dumper->cur_seq) {
+			/* messages are gone, move to first available one */
+			dumper->cur_seq = info.seq;
+		}
 	}
 
 	/* last entry */
diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringbuffer.h
index 5dc9d022db07..73cc80e01cef 100644
--- a/kernel/printk/printk_ringbuffer.h
+++ b/kernel/printk/printk_ringbuffer.h
@@ -287,7 +287,7 @@ _DEFINE_PRINTKRB(name, descbits, avgtextbits, &_##name##_text[0])
 /* Writer Interface */
 
 /**
- * prb_rec_init_wd() - Initialize a buffer for writing records.
+ * prb_rec_init_wr() - Initialize a buffer for writing records.
  *
  * @r:             The record to initialize.
  * @text_buf_size: The needed text buffer size.
diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index a0e6f746de6c..2e9e3ed7d63e 100644
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -45,6 +45,8 @@ struct printk_safe_seq_buf {
 static DEFINE_PER_CPU(struct printk_safe_seq_buf, safe_print_seq);
 static DEFINE_PER_CPU(int, printk_context);
 
+static DEFINE_RAW_SPINLOCK(safe_read_lock);
+
 #ifdef CONFIG_PRINTK_NMI
 static DEFINE_PER_CPU(struct printk_safe_seq_buf, nmi_print_seq);
 #endif
@@ -180,8 +182,6 @@ static void report_message_lost(struct printk_safe_seq_buf *s)
  */
 static void __printk_safe_flush(struct irq_work *work)
 {
-	static raw_spinlock_t read_lock =
-		__RAW_SPIN_LOCK_INITIALIZER(read_lock);
 	struct printk_safe_seq_buf *s =
 		container_of(work, struct printk_safe_seq_buf, work);
 	unsigned long flags;
@@ -195,7 +195,7 @@ static void __printk_safe_flush(struct irq_work *work)
 	 * different CPUs. This is especially important when printing
 	 * a backtrace.
 	 */
-	raw_spin_lock_irqsave(&read_lock, flags);
+	raw_spin_lock_irqsave(&safe_read_lock, flags);
 
 	i = 0;
 more:
@@ -232,7 +232,7 @@ more:
 
 out:
 	report_message_lost(s);
-	raw_spin_unlock_irqrestore(&read_lock, flags);
+	raw_spin_unlock_irqrestore(&safe_read_lock, flags);
 }
 
 /**
@@ -278,6 +278,14 @@ void printk_safe_flush_on_panic(void)
 		raw_spin_lock_init(&logbuf_lock);
 	}
 
+	if (raw_spin_is_locked(&safe_read_lock)) {
+		if (num_online_cpus() > 1)
+			return;
+
+		debug_locks_off();
+		raw_spin_lock_init(&safe_read_lock);
+	}
+
 	printk_safe_flush();
 }