diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
index 532f226377831d89c592696df54794eaab311a8f..1ef55f4b389a2990ff3dc6edc8f86f43047b3ec8 100644
--- a/arch/powerpc/kernel/nvram_64.c
+++ b/arch/powerpc/kernel/nvram_64.c
@@ -73,7 +73,8 @@ static const char *nvram_os_partitions[] = {
 };
 
 static void oops_to_nvram(struct kmsg_dumper *dumper,
-			  enum kmsg_dump_reason reason);
+			  enum kmsg_dump_reason reason,
+			  struct kmsg_dumper_iter *iter);
 
 static struct kmsg_dumper nvram_kmsg_dumper = {
 	.dump = oops_to_nvram
@@ -643,7 +644,8 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
  * partition.  If that's too much, go back and capture uncompressed text.
  */
 static void oops_to_nvram(struct kmsg_dumper *dumper,
-			  enum kmsg_dump_reason reason)
+			  enum kmsg_dump_reason reason,
+			  struct kmsg_dumper_iter *iter)
 {
 	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
 	static unsigned int oops_count = 0;
@@ -681,13 +683,13 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
 		return;
 
 	if (big_oops_buf) {
-		kmsg_dump_get_buffer(dumper, false,
+		kmsg_dump_get_buffer(iter, false,
 				     big_oops_buf, big_oops_buf_sz, &text_len);
 		rc = zip_oops(text_len);
 	}
 	if (rc != 0) {
-		kmsg_dump_rewind(dumper);
-		kmsg_dump_get_buffer(dumper, false,
+		kmsg_dump_rewind(iter);
+		kmsg_dump_get_buffer(iter, false,
 				     oops_data, oops_data_sz, &text_len);
 		err_type = ERR_TYPE_KERNEL_PANIC;
 		oops_hdr->version = cpu_to_be16(OOPS_HDR_VERSION);
diff --git a/arch/powerpc/platforms/powernv/opal-kmsg.c b/arch/powerpc/platforms/powernv/opal-kmsg.c
index 6c3bc4b4da9834966f7fd19eb28454ac33988b9e..ec862846bc82cbb1c2681f0ba3a7ef271c311878 100644
--- a/arch/powerpc/platforms/powernv/opal-kmsg.c
+++ b/arch/powerpc/platforms/powernv/opal-kmsg.c
@@ -20,7 +20,8 @@
  * message, it just ensures that OPAL completely flushes the console buffer.
  */
 static void kmsg_dump_opal_console_flush(struct kmsg_dumper *dumper,
-				     enum kmsg_dump_reason reason)
+					 enum kmsg_dump_reason reason,
+					 struct kmsg_dumper_iter *iter)
 {
 	/*
 	 * Outside of a panic context the pollers will continue to run,
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 5559edf36756c429cae207f58312ca85feced26b..b71690e8245b5998cd893e65bdfd8c8556612bdf 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -3005,7 +3005,7 @@ print_address(unsigned long addr)
 static void
 dump_log_buf(void)
 {
-	struct kmsg_dumper dumper = { .active = 1 };
+	struct kmsg_dumper_iter iter = { .active = 1 };
 	unsigned char buf[128];
 	size_t len;
 
@@ -3017,9 +3017,9 @@ dump_log_buf(void)
 	catch_memory_errors = 1;
 	sync();
 
-	kmsg_dump_rewind_nolock(&dumper);
+	kmsg_dump_rewind_nolock(&iter);
 	xmon_start_pagination();
-	while (kmsg_dump_get_line_nolock(&dumper, false, buf, sizeof(buf), &len)) {
+	while (kmsg_dump_get_line_nolock(&iter, false, buf, sizeof(buf), &len)) {
 		buf[len] = '\0';
 		printf("%s", buf);
 	}
diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
index e4abac6c9727cc274647b47da116c1dfeae4e6d8..f38349ad00ead0693091d2768940859dbc8039e4 100644
--- a/arch/um/kernel/kmsg_dump.c
+++ b/arch/um/kernel/kmsg_dump.c
@@ -6,7 +6,8 @@
 #include <os.h>
 
 static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
-				enum kmsg_dump_reason reason)
+				enum kmsg_dump_reason reason,
+				struct kmsg_dumper_iter *iter)
 {
 	static char line[1024];
 	struct console *con;
@@ -25,7 +26,7 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 		return;
 
 	printf("kmsg_dump:\n");
-	while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len)) {
+	while (kmsg_dump_get_line(iter, true, line, sizeof(line), &len)) {
 		line[len] = '\0';
 		printf("%s", line);
 	}
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 5d820037e29183902361a5af893ed2b23eb74675..13d56054e3d2ace17ec69b4c1d4d3e85644195e9 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1359,7 +1359,8 @@ static void vmbus_isr(void)
  * buffer and call into Hyper-V to transfer the data.
  */
 static void hv_kmsg_dump(struct kmsg_dumper *dumper,
-			 enum kmsg_dump_reason reason)
+			 enum kmsg_dump_reason reason,
+			 struct kmsg_dumper_iter *iter)
 {
 	size_t bytes_written;
 	phys_addr_t panic_pa;
@@ -1374,7 +1375,7 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper,
 	 * Write dump contents to the page. No need to synchronize; panic should
 	 * be single-threaded.
 	 */
-	kmsg_dump_get_buffer(dumper, false, hv_panic_page, HV_HYP_PAGE_SIZE,
+	kmsg_dump_get_buffer(iter, false, hv_panic_page, HV_HYP_PAGE_SIZE,
 			     &bytes_written);
 	if (bytes_written)
 		hyperv_report_panic_msg(panic_pa, bytes_written);
diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
index 774970bfcf859621148347f5c453dcf41f3aa0be..6bc2c728adb73a4c8bf82916d027bb9a0b035552 100644
--- a/drivers/mtd/mtdoops.c
+++ b/drivers/mtd/mtdoops.c
@@ -267,7 +267,8 @@ static void find_next_position(struct mtdoops_context *cxt)
 }
 
 static void mtdoops_do_dump(struct kmsg_dumper *dumper,
-			    enum kmsg_dump_reason reason)
+			    enum kmsg_dump_reason reason,
+			    struct kmsg_dumper_iter *iter)
 {
 	struct mtdoops_context *cxt = container_of(dumper,
 			struct mtdoops_context, dump);
@@ -276,7 +277,7 @@ static void mtdoops_do_dump(struct kmsg_dumper *dumper,
 	if (reason == KMSG_DUMP_OOPS && !dump_oops)
 		return;
 
-	kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
+	kmsg_dump_get_buffer(iter, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
 			     record_size - MTDOOPS_HEADER_SIZE, NULL);
 
 	if (reason != KMSG_DUMP_OOPS) {
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index 17d7bc27f41a37853404e8fa0ac6e607de419a1a..567decf3b53f00c2992f086fd1b083925fcdff3b 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -382,7 +382,8 @@ void pstore_record_init(struct pstore_record *record,
  * end of the buffer.
  */
 static void pstore_do_dump(struct kmsg_dumper *dumper,
-			enum kmsg_dump_reason reason, struct pstore_info *psinfo, int pos)
+			enum kmsg_dump_reason reason, 
+			struct kmsg_dumper_iter *iter, struct pstore_info *psinfo, int pos)
 {
 	unsigned long	total = 0;
 	const char	*why;
@@ -432,7 +433,7 @@ static void pstore_do_dump(struct kmsg_dumper *dumper,
 		dst_size -= header_size;
 
 		/* Write dump contents. */
-		if (!kmsg_dump_get_buffer(dumper, true, dst + header_size,
+		if (!kmsg_dump_get_buffer(iter, true, dst + header_size,
 					  dst_size, &dump_size))
 			break;
 
@@ -465,14 +466,15 @@ static void pstore_do_dump(struct kmsg_dumper *dumper,
 }
 
 static void pstore_dump(struct kmsg_dumper *dumper,
-			enum kmsg_dump_reason reason)
+			enum kmsg_dump_reason reason,
+			struct kmsg_dumper_iter *iter)
 {
 	struct pstore_info_list *entry;
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(entry, &psback->list_entry, list)
 		if (entry->psi->flags & PSTORE_FLAGS_DMESG)
-			pstore_do_dump(dumper, reason, entry->psi, entry->index);
+			pstore_do_dump(dumper, reason, iter, entry->psi, entry->index);
 	rcu_read_unlock();
 }
 
diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 3378bcbe585eac4e76e93c768c287f6fd9c2eab8..2fdb10ab179948e57e5b82e9f36c42ccba8b61d0 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -29,6 +29,18 @@ enum kmsg_dump_reason {
 	KMSG_DUMP_MAX
 };
 
+/**
+ * struct kmsg_dumper_iter - iterator for kernel crash message dumper
+ * @active:	Flag that specifies if this is currently dumping
+ * @cur_seq:	Points to the oldest message to dump (private)
+ * @next_seq:	Points after the newest message to dump (private)
+ */
+struct kmsg_dumper_iter {
+	bool	active;
+	u64	cur_seq;
+	u64	next_seq;
+};
+
 /**
  * struct kmsg_dumper - kernel crash message dumper structure
  * @list:	Entry in the dumper list (private)
@@ -39,33 +51,27 @@ enum kmsg_dump_reason {
  */
 struct kmsg_dumper {
 	struct list_head list;
-	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason);
+	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason,
+		     struct kmsg_dumper_iter *iter);
 	enum kmsg_dump_reason max_reason;
-	bool active;
 	bool registered;
-
-	/* private state of the kmsg iterator */
-	u32 cur_idx;
-	u32 next_idx;
-	u64 cur_seq;
-	u64 next_seq;
 };
 
 #ifdef CONFIG_PRINTK
 void kmsg_dump(enum kmsg_dump_reason reason);
 
-bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line_nolock(struct kmsg_dumper_iter *iter, bool syslog,
 			       char *line, size_t size, size_t *len);
 
-bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line(struct kmsg_dumper_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len);
 
-bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
-			  char *buf, size_t size, size_t *len);
+bool kmsg_dump_get_buffer(struct kmsg_dumper_iter *iter, bool syslog,
+			  char *buf, size_t size, size_t *len_out);
 
-void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper);
+void kmsg_dump_rewind_nolock(struct kmsg_dumper_iter *iter);
 
-void kmsg_dump_rewind(struct kmsg_dumper *dumper);
+void kmsg_dump_rewind(struct kmsg_dumper_iter *dumper_iter);
 
 int kmsg_dump_register(struct kmsg_dumper *dumper);
 
@@ -77,30 +83,30 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason)
 {
 }
 
-static inline bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper,
+static inline bool kmsg_dump_get_line_nolock(struct kmsg_dumper_iter *iter,
 					     bool syslog, const char *line,
 					     size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+static inline bool kmsg_dump_get_line(struct kmsg_dumper_iter *iter, bool syslog,
 				const char *line, size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+static inline bool kmsg_dump_get_buffer(struct kmsg_dumper_iter *iter, bool syslog,
 					char *buf, size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
+static inline void kmsg_dump_rewind_nolock(struct kmsg_dumper_iter *iter)
 {
 }
 
-static inline void kmsg_dump_rewind(struct kmsg_dumper *dumper)
+static inline void kmsg_dump_rewind(struct kmsg_dumper_iter *iter)
 {
 }
 
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 4e09fab52faf50beed7f4af7de696d4689c16d40..048baadd7a41c21af0f4c6037bf67eb6a298eb20 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2157,7 +2157,7 @@ static int kdb_dmesg(int argc, const char **argv)
 	int adjust = 0;
 	int n = 0;
 	int skip = 0;
-	struct kmsg_dumper dumper = { .active = 1 };
+	struct kmsg_dumper_iter iter = { .active = 1 };
 	size_t len;
 	char buf[201];
 
@@ -2182,8 +2182,8 @@ static int kdb_dmesg(int argc, const char **argv)
 		kdb_set(2, setargs);
 	}
 
-	kmsg_dump_rewind_nolock(&dumper);
-	while (kmsg_dump_get_line_nolock(&dumper, 1, NULL, 0, NULL))
+	kmsg_dump_rewind_nolock(&iter);
+	while (kmsg_dump_get_line_nolock(&iter, 1, NULL, 0, NULL))
 		n++;
 
 	if (lines < 0) {
@@ -2215,8 +2215,8 @@ static int kdb_dmesg(int argc, const char **argv)
 	if (skip >= n || skip < 0)
 		return 0;
 
-	kmsg_dump_rewind_nolock(&dumper);
-	while (kmsg_dump_get_line_nolock(&dumper, 1, buf, sizeof(buf), &len)) {
+	kmsg_dump_rewind_nolock(&iter);
+	while (kmsg_dump_get_line_nolock(&iter, 1, buf, sizeof(buf), &len)) {
 		if (skip) {
 			skip--;
 			continue;
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index dcb1354154cca953d0ffb9ec65095f359a6222a1..41acad5250c6d19fe07f05637ab30c38f577c5a4 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -403,8 +403,12 @@ DEFINE_RAW_SPINLOCK(logbuf_lock);
 		printk_safe_exit_irqrestore(flags);	\
 	} while (0)
 
+/* syslog_lock protects syslog_* variables and write access to clear_seq. */
+static DEFINE_RAW_SPINLOCK(syslog_lock);
+
 #ifdef CONFIG_PRINTK
 DECLARE_WAIT_QUEUE_HEAD(log_wait);
+/* All 3 protected by @syslog_lock. */
 /* the next printk record to read by syslog(READ) or /proc/kmsg */
 static u64 syslog_seq;
 static size_t syslog_partial;
@@ -415,16 +419,34 @@ static u64 console_seq;
 static u64 exclusive_console_stop_seq;
 static unsigned long console_dropped;
 
-/* the next printk record to read after the last 'clear' command */
-static u64 clear_seq;
+struct latched_seq {
+	seqcount_latch_t	latch;
+	u64			val[2];
+};
+
+/*
+ * The next printk record to read after the last 'clear' command. There are
+ * two copies (updated with seqcount_latch) so that reads can locklessly
+ * access a valid value. Writers are synchronized by @syslog_lock.
+ */
+static struct latched_seq clear_seq = {
+	.latch		= SEQCNT_LATCH_ZERO(clear_seq.latch),
+	.val[0]		= 0,
+	.val[1]		= 0,
+};
 
 #ifdef CONFIG_PRINTK_CALLER
 #define PREFIX_MAX		48
 #else
 #define PREFIX_MAX		32
 #endif
+
+/* the maximum size allowed to be reserved for a record */
 #define LOG_LINE_MAX		(1024 - PREFIX_MAX)
 
+/* the maximum size of a formatted record (i.e. with prefix added per line) */
+#define CONSOLE_LOG_MAX		4096
+
 #define LOG_LEVEL(v)		((v) & 0x07)
 #define LOG_FACILITY(v)		((v) >> 3 & 0xff)
 
@@ -465,6 +487,31 @@ bool printk_percpu_data_ready(void)
 	return __printk_percpu_data_ready;
 }
 
+/* Must be called under syslog_lock. */
+static void latched_seq_write(struct latched_seq *ls, u64 val)
+{
+	raw_write_seqcount_latch(&ls->latch);
+	ls->val[0] = val;
+	raw_write_seqcount_latch(&ls->latch);
+	ls->val[1] = val;
+}
+
+/* Can be called from any context. */
+static u64 latched_seq_read_nolock(struct latched_seq *ls)
+{
+	unsigned int seq;
+	unsigned int idx;
+	u64 val;
+
+	do {
+		seq = raw_read_seqcount_latch(&ls->latch);
+		idx = seq & 0x1;
+		val = ls->val[idx];
+	} while (read_seqcount_latch_retry(&ls->latch, seq));
+
+	return val;
+}
+
 /* Return log buffer address */
 char *log_buf_addr_get(void)
 {
@@ -504,52 +551,6 @@ static void truncate_msg(u16 *text_len, u16 *trunc_msg_len)
 		*trunc_msg_len = 0;
 }
 
-/* insert record into the buffer, discard old ones, update heads */
-static int log_store(u32 caller_id, int facility, int level,
-		     enum log_flags flags, u64 ts_nsec,
-		     const struct dev_printk_info *dev_info,
-		     const char *text, u16 text_len)
-{
-	struct prb_reserved_entry e;
-	struct printk_record r;
-	u16 trunc_msg_len = 0;
-
-	prb_rec_init_wr(&r, text_len);
-
-	if (!prb_reserve(&e, prb, &r)) {
-		/* truncate the message if it is too long for empty buffer */
-		truncate_msg(&text_len, &trunc_msg_len);
-		prb_rec_init_wr(&r, text_len + trunc_msg_len);
-		/* survive when the log buffer is too small for trunc_msg */
-		if (!prb_reserve(&e, prb, &r))
-			return 0;
-	}
-
-	/* fill message */
-	memcpy(&r.text_buf[0], text, text_len);
-	if (trunc_msg_len)
-		memcpy(&r.text_buf[text_len], trunc_msg, trunc_msg_len);
-	r.info->text_len = text_len + trunc_msg_len;
-	r.info->facility = facility;
-	r.info->level = level & 7;
-	r.info->flags = flags & 0x1f;
-	if (ts_nsec > 0)
-		r.info->ts_nsec = ts_nsec;
-	else
-		r.info->ts_nsec = local_clock();
-	r.info->caller_id = caller_id;
-	if (dev_info)
-		memcpy(&r.info->dev_info, dev_info, sizeof(r.info->dev_info));
-
-	/* A message without a trailing newline can be continued. */
-	if (!(flags & LOG_NEWLINE))
-		prb_commit(&e);
-	else
-		prb_final_commit(&e);
-
-	return (text_len + trunc_msg_len);
-}
-
 int dmesg_restrict = IS_ENABLED(CONFIG_SECURITY_DMESG_RESTRICT);
 
 static int syslog_action_restricted(int type)
@@ -678,7 +679,7 @@ static ssize_t msg_print_ext_body(char *buf, size_t size,
 
 /* /dev/kmsg - userspace message inject/listen interface */
 struct devkmsg_user {
-	u64 seq;
+	atomic64_t seq;
 	struct ratelimit_state rs;
 	struct mutex lock;
 	char buf[CONSOLE_EXT_LOG_MAX];
@@ -780,7 +781,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 		return ret;
 
 	logbuf_lock_irq();
-	if (!prb_read_valid(prb, user->seq, r)) {
+	if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
 		if (file->f_flags & O_NONBLOCK) {
 			ret = -EAGAIN;
 			logbuf_unlock_irq();
@@ -789,15 +790,15 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 
 		logbuf_unlock_irq();
 		ret = wait_event_interruptible(log_wait,
-					prb_read_valid(prb, user->seq, r));
+				prb_read_valid(prb, atomic64_read(&user->seq), r));
 		if (ret)
 			goto out;
 		logbuf_lock_irq();
 	}
 
-	if (r->info->seq != user->seq) {
+	if (r->info->seq != atomic64_read(&user->seq)) {
 		/* our last seen message is gone, return error and reset */
-		user->seq = r->info->seq;
+		atomic64_set(&user->seq, r->info->seq);
 		ret = -EPIPE;
 		logbuf_unlock_irq();
 		goto out;
@@ -808,7 +809,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 				  &r->text_buf[0], r->info->text_len,
 				  &r->info->dev_info);
 
-	user->seq = r->info->seq + 1;
+	atomic64_set(&user->seq, r->info->seq + 1);
 	logbuf_unlock_irq();
 
 	if (len > count) {
@@ -848,7 +849,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
 	switch (whence) {
 	case SEEK_SET:
 		/* the first record */
-		user->seq = prb_first_valid_seq(prb);
+		atomic64_set(&user->seq, prb_first_valid_seq(prb));
 		break;
 	case SEEK_DATA:
 		/*
@@ -856,11 +857,11 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
 		 * like issued by 'dmesg -c'. Reading /dev/kmsg itself
 		 * changes no global state, and does not clear anything.
 		 */
-		user->seq = clear_seq;
+		atomic64_set(&user->seq, latched_seq_read_nolock(&clear_seq));
 		break;
 	case SEEK_END:
 		/* after the last record */
-		user->seq = prb_next_seq(prb);
+		atomic64_set(&user->seq, prb_next_seq(prb));
 		break;
 	default:
 		ret = -EINVAL;
@@ -883,7 +884,7 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
 	logbuf_lock_irq();
 	if (prb_read_valid_info(prb, user->seq, &info, NULL)) {
 		/* return error when data has vanished underneath us */
-		if (info.seq != user->seq)
+		if (info.seq != atomic64_read(&user->seq))
 			ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
 		else
 			ret = EPOLLIN|EPOLLRDNORM;
@@ -922,7 +923,7 @@ static int devkmsg_open(struct inode *inode, struct file *file)
 			&user->text_buf[0], sizeof(user->text_buf));
 
 	logbuf_lock_irq();
-	user->seq = prb_first_valid_seq(prb);
+	atomic64_set(&user->seq, prb_first_valid_seq(prb));
 	logbuf_unlock_irq();
 
 	file->private_data = user;
@@ -1015,6 +1016,9 @@ void log_buf_vmcoreinfo_setup(void)
 
 	VMCOREINFO_SIZE(atomic_long_t);
 	VMCOREINFO_TYPE_OFFSET(atomic_long_t, counter);
+
+	VMCOREINFO_STRUCT_SIZE(latched_seq);
+	VMCOREINFO_OFFSET(latched_seq, val);
 }
 #endif
 
@@ -1186,7 +1190,7 @@ void __init setup_log_buf(int early)
 		 new_descs, ilog2(new_descs_count),
 		 new_infos);
 
-	logbuf_lock_irqsave(flags);
+	printk_safe_enter_irqsave(flags);
 
 	log_buf_len = new_log_buf_len;
 	log_buf = new_log_buf;
@@ -1203,7 +1207,7 @@ void __init setup_log_buf(int early)
 	 */
 	prb = &printk_rb_dynamic;
 
-	logbuf_unlock_irqrestore(flags);
+	printk_safe_exit_irqrestore(flags);
 
 	if (seq != prb_next_seq(&printk_rb_static)) {
 		pr_err("dropped %llu messages\n",
@@ -1481,6 +1485,50 @@ static size_t get_record_print_text_size(struct printk_info *info,
 	return ((prefix_len * line_count) + info->text_len + 1);
 }
 
+/*
+ * Beginning with @start_seq, find the first record where it and all following
+ * records up to (but not including) @max_seq fit into @size.
+ *
+ * @max_seq is simply an upper bound and does not need to exist. If the caller
+ * does not require an upper bound, -1 can be used for @max_seq.
+ */
+static u64 find_first_fitting_seq(u64 start_seq, u64 max_seq, size_t size,
+				  bool syslog, bool time)
+{
+	struct printk_info info;
+	unsigned int line_count;
+	size_t len = 0;
+	u64 seq;
+
+	/* Determine the size of the records up to @max_seq. */
+	prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
+		if (info.seq >= max_seq)
+			break;
+		len += get_record_print_text_size(&info, line_count, syslog, time);
+	}
+
+	/*
+	 * Adjust the upper bound for the next loop to avoid subtracting
+	 * lengths that were never added.
+	 */
+	if (seq < max_seq)
+		max_seq = seq;
+
+	/*
+	 * Move first record forward until length fits into the buffer. Ignore
+	 * newest messages that were not counted in the above cycle. Messages
+	 * might appear and get lost in the meantime. This is a best effort
+	 * that prevents an infinite loop that could occur with a retry.
+	 */
+	prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
+		if (len <= size || info.seq >= max_seq)
+			break;
+		len -= get_record_print_text_size(&info, line_count, syslog, time);
+	}
+
+	return seq;
+}
+
 static int syslog_print(char __user *buf, int size)
 {
 	struct printk_info info;
@@ -1488,18 +1536,20 @@ static int syslog_print(char __user *buf, int size)
 	char *text;
 	int len = 0;
 
-	text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
+	text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
 	if (!text)
 		return -ENOMEM;
 
-	prb_rec_init_rd(&r, &info, text, LOG_LINE_MAX + PREFIX_MAX);
+	prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
 
 	while (size > 0) {
 		size_t n;
 		size_t skip;
 
 		logbuf_lock_irq();
+		raw_spin_lock(&syslog_lock);
 		if (!prb_read_valid(prb, syslog_seq, &r)) {
+			raw_spin_unlock(&syslog_lock);
 			logbuf_unlock_irq();
 			break;
 		}
@@ -1529,6 +1579,7 @@ static int syslog_print(char __user *buf, int size)
 			syslog_partial += n;
 		} else
 			n = 0;
+		raw_spin_unlock(&syslog_lock);
 		logbuf_unlock_irq();
 
 		if (!n)
@@ -1552,14 +1603,13 @@ static int syslog_print(char __user *buf, int size)
 static int syslog_print_all(char __user *buf, int size, bool clear)
 {
 	struct printk_info info;
-	unsigned int line_count;
 	struct printk_record r;
 	char *text;
 	int len = 0;
 	u64 seq;
 	bool time;
 
-	text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
+	text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
 	if (!text)
 		return -ENOMEM;
 
@@ -1569,17 +1619,10 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	 * Find first record that fits, including all following records,
 	 * into the user-provided buffer for this dump.
 	 */
-	prb_for_each_info(clear_seq, prb, seq, &info, &line_count)
-		len += get_record_print_text_size(&info, line_count, true, time);
+	seq = find_first_fitting_seq(latched_seq_read_nolock(&clear_seq), -1,
+				     size, true, time);
 
-	/* move first record forward until length fits into the buffer */
-	prb_for_each_info(clear_seq, prb, seq, &info, &line_count) {
-		if (len <= size)
-			break;
-		len -= get_record_print_text_size(&info, line_count, true, time);
-	}
-
-	prb_rec_init_rd(&r, &info, text, LOG_LINE_MAX + PREFIX_MAX);
+	prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
 
 	len = 0;
 	prb_for_each_record(seq, prb, seq, &r) {
@@ -1603,8 +1646,11 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 			break;
 	}
 
-	if (clear)
-		clear_seq = seq;
+	if (clear) {
+		raw_spin_lock(&syslog_lock);
+		latched_seq_write(&clear_seq, seq);
+		raw_spin_unlock(&syslog_lock);
+	}
 	logbuf_unlock_irq();
 
 	kfree(text);
@@ -1614,10 +1660,24 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 static void syslog_clear(void)
 {
 	logbuf_lock_irq();
-	clear_seq = prb_next_seq(prb);
+	raw_spin_lock(&syslog_lock);
+	latched_seq_write(&clear_seq, prb_next_seq(prb));
+	raw_spin_unlock(&syslog_lock);
 	logbuf_unlock_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;
+}
+
 int do_syslog(int type, char __user *buf, int len, int source)
 {
 	struct printk_info info;
@@ -1641,8 +1701,9 @@ 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, syslog_seq, NULL));
+				prb_read_valid(prb, read_syslog_seq_irq(), NULL));
 		if (error)
 			return error;
 		error = syslog_print(buf, len);
@@ -1691,8 +1752,10 @@ 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();
+		raw_spin_lock(&syslog_lock);
 		if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
 			/* No unread messages. */
+			raw_spin_unlock(&syslog_lock);
 			logbuf_unlock_irq();
 			return 0;
 		}
@@ -1721,6 +1784,7 @@ int do_syslog(int type, char __user *buf, int len, int source)
 			}
 			error -= syslog_partial;
 		}
+		raw_spin_unlock(&syslog_lock);
 		logbuf_unlock_irq();
 		break;
 	/* Size of the log buffer */
@@ -1954,83 +2018,177 @@ static inline u32 printk_caller_id(void)
 		0x80000000 + raw_smp_processor_id();
 }
 
-static size_t log_output(int facility, int level, enum log_flags lflags,
-			 const struct dev_printk_info *dev_info,
-			 char *text, size_t text_len)
+/**
+ * parse_prefix - Parse level and control flags.
+ *
+ * @text:     The terminated text message.
+ * @level:    A pointer to the current level value, will be updated.
+ * @lflags:   A pointer to the current log flags, will be updated.
+ *
+ * @level may be NULL if the caller is not interested in the parsed value.
+ * Otherwise the variable pointed to by @level must be set to
+ * LOGLEVEL_DEFAULT in order to be updated with the parsed value.
+ *
+ * @lflags may be NULL if the caller is not interested in the parsed value.
+ * Otherwise the variable pointed to by @lflags will be OR'd with the parsed
+ * value.
+ *
+ * Return: The length of the parsed level and control flags.
+ */
+static u16 parse_prefix(char *text, int *level, enum log_flags *lflags)
 {
-	const u32 caller_id = printk_caller_id();
+	u16 prefix_len = 0;
+	int kern_level;
 
-	if (lflags & LOG_CONT) {
-		struct prb_reserved_entry e;
-		struct printk_record r;
+	while (*text) {
+		kern_level = printk_get_level(text);
+		if (!kern_level)
+			break;
 
-		prb_rec_init_wr(&r, text_len);
-		if (prb_reserve_in_last(&e, prb, &r, caller_id, LOG_LINE_MAX)) {
-			memcpy(&r.text_buf[r.info->text_len], text, text_len);
-			r.info->text_len += text_len;
-			if (lflags & LOG_NEWLINE) {
-				r.info->flags |= LOG_NEWLINE;
-				prb_final_commit(&e);
-			} else {
-				prb_commit(&e);
-			}
-			return text_len;
+		switch (kern_level) {
+		case '0' ... '7':
+			if (level && *level == LOGLEVEL_DEFAULT)
+				*level = kern_level - '0';
+			break;
+		case 'c':	/* KERN_CONT */
+			if (lflags)
+				*lflags |= LOG_CONT;
 		}
+
+		prefix_len += 2;
+		text += 2;
 	}
 
-	/* Store it in the record log */
-	return log_store(caller_id, facility, level, lflags, 0,
-			 dev_info, text, text_len);
+	return prefix_len;
 }
 
-/* Must be called under logbuf_lock. */
+static u16 printk_sprint(char *text, u16 size, int facility, enum log_flags *lflags,
+			 const char *fmt, va_list args)
+{
+	u16 text_len;
+
+	text_len = vscnprintf(text, size, fmt, args);
+
+	/* Mark and strip a trailing newline. */
+	if (text_len && text[text_len - 1] == '\n') {
+		text_len--;
+		*lflags |= LOG_NEWLINE;
+	}
+
+	/* Strip log level and control flags. */
+	if (facility == 0) {
+		u16 prefix_len;
+
+		prefix_len = parse_prefix(text, NULL, NULL);
+		if (prefix_len) {
+			text_len -= prefix_len;
+			memmove(text, text + prefix_len, text_len);
+		}
+	}
+
+	return text_len;
+}
+
+__printf(4, 0)
 int vprintk_store(int facility, int level,
 		  const struct dev_printk_info *dev_info,
 		  const char *fmt, va_list args)
 {
-	static char textbuf[LOG_LINE_MAX];
-	char *text = textbuf;
-	size_t text_len;
+	const u32 caller_id = printk_caller_id();
+	struct prb_reserved_entry e;
 	enum log_flags lflags = 0;
+	struct printk_record r;
+	u16 trunc_msg_len = 0;
+	char prefix_buf[8];
+	u16 reserve_size;
+	va_list args2;
+	u16 text_len;
+	u64 ts_nsec;
 
 	/*
-	 * The printf needs to come first; we need the syslog
-	 * prefix which might be passed-in as a parameter.
+	 * Since the duration of printk() can vary depending on the message
+	 * and state of the ringbuffer, grab the timestamp now so that it is
+	 * close to the call of printk(). This provides a more deterministic
+	 * timestamp with respect to the caller.
 	 */
-	text_len = vscnprintf(text, sizeof(textbuf), fmt, args);
+	ts_nsec = local_clock();
 
-	/* mark and strip a trailing newline */
-	if (text_len && text[text_len-1] == '\n') {
-		text_len--;
+	/*
+	 * 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
+	 * later the vscnprintf() into the reserved buffer has room for the
+	 * terminating '\0', which is not counted by vsnprintf().
+	 */
+	va_copy(args2, args);
+	reserve_size = vsnprintf(&prefix_buf[0], sizeof(prefix_buf), fmt, args2) + 1;
+	va_end(args2);
+
+	if (reserve_size > LOG_LINE_MAX)
+		reserve_size = LOG_LINE_MAX;
+
+	/* Extract log level or control flags. */
+	if (facility == 0)
+		parse_prefix(&prefix_buf[0], &level, &lflags);
+
+	if (level == LOGLEVEL_DEFAULT)
+		level = default_message_loglevel;
+
+	if (dev_info)
 		lflags |= LOG_NEWLINE;
-	}
 
-	/* strip kernel syslog prefix and extract log level or control flags */
-	if (facility == 0) {
-		int kern_level;
+	if (lflags & LOG_CONT) {
+		prb_rec_init_wr(&r, reserve_size);
+		if (prb_reserve_in_last(&e, prb, &r, caller_id, LOG_LINE_MAX)) {
+			text_len = printk_sprint(&r.text_buf[r.info->text_len], reserve_size,
+						 facility, &lflags, fmt, args);
+			r.info->text_len += text_len;
 
-		while ((kern_level = printk_get_level(text)) != 0) {
-			switch (kern_level) {
-			case '0' ... '7':
-				if (level == LOGLEVEL_DEFAULT)
-					level = kern_level - '0';
-				break;
-			case 'c':	/* KERN_CONT */
-				lflags |= LOG_CONT;
+			if (lflags & LOG_NEWLINE) {
+				r.info->flags |= LOG_NEWLINE;
+				prb_final_commit(&e);
+			} else {
+				prb_commit(&e);
 			}
 
-			text_len -= 2;
-			text += 2;
+			return text_len;
 		}
 	}
 
-	if (level == LOGLEVEL_DEFAULT)
-		level = default_message_loglevel;
+	/*
+	 * Explicitly initialize the record before every prb_reserve() call.
+	 * prb_reserve_in_last() and prb_reserve() purposely invalidate the
+	 * structure when they fail.
+	 */
+	prb_rec_init_wr(&r, reserve_size);
+	if (!prb_reserve(&e, prb, &r)) {
+		/* truncate the message if it is too long for empty buffer */
+		truncate_msg(&reserve_size, &trunc_msg_len);
 
+		prb_rec_init_wr(&r, reserve_size + trunc_msg_len);
+		if (!prb_reserve(&e, prb, &r))
+			return 0;
+	}
+
+	/* fill message */
+	text_len = printk_sprint(&r.text_buf[0], reserve_size, facility, &lflags, fmt, args);
+	if (trunc_msg_len)
+		memcpy(&r.text_buf[text_len], trunc_msg, trunc_msg_len);
+	r.info->text_len = text_len + trunc_msg_len;
+	r.info->facility = facility;
+	r.info->level = level & 7;
+	r.info->flags = lflags & 0x1f;
+	r.info->ts_nsec = ts_nsec;
+	r.info->caller_id = caller_id;
 	if (dev_info)
-		lflags |= LOG_NEWLINE;
+		memcpy(&r.info->dev_info, dev_info, sizeof(r.info->dev_info));
+
+	/* A message without a trailing newline can be continued. */
+	if (!(lflags & LOG_NEWLINE))
+		prb_commit(&e);
+	else
+		prb_final_commit(&e);
 
-	return log_output(facility, level, lflags, dev_info, text, text_len);
+	return (text_len + trunc_msg_len);
 }
 
 asmlinkage int vprintk_emit(int facility, int level,
@@ -2059,10 +2217,9 @@ asmlinkage int vprintk_emit(int facility, int level,
 	boot_delay_msec(level);
 	printk_delay();
 
-	/* This stops the holder of console_sem just where we want him */
-	logbuf_lock_irqsave(flags);
+	printk_safe_enter_irqsave(flags);
 	printed_len = vprintk_store(facility, level, dev_info, fmt, args);
-	logbuf_unlock_irqrestore(flags);
+	printk_safe_exit_irqrestore(flags);
 
 	/* If called from the scheduler, we can not call up(). */
 	if (!in_sched) {
@@ -2135,8 +2292,7 @@ EXPORT_SYMBOL(printk);
 
 #else /* CONFIG_PRINTK */
 
-#define LOG_LINE_MAX		0
-#define PREFIX_MAX		0
+#define CONSOLE_LOG_MAX		0
 #define printk_time		false
 
 #define prb_read_valid(rb, seq, r)	false
@@ -2473,7 +2629,7 @@ static inline int can_use_console(void)
 void console_unlock(void)
 {
 	static char ext_text[CONSOLE_EXT_LOG_MAX];
-	static char text[LOG_LINE_MAX + PREFIX_MAX];
+	static char text[CONSOLE_LOG_MAX];
 	static int panic_console_dropped;
 	unsigned long flags;
 	bool do_cond_resched, retry;
@@ -2923,7 +3079,12 @@ void register_console(struct console *newcon)
 		 */
 		exclusive_console = newcon;
 		exclusive_console_stop_seq = console_seq;
+
+		/* Get a consistent copy of @syslog_seq. */
+		raw_spin_lock(&syslog_lock);
 		console_seq = syslog_seq;
+		raw_spin_unlock(&syslog_lock);
+
 		logbuf_unlock_irqrestore(flags);
 	}
 	console_unlock();
@@ -3289,6 +3450,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
  */
 void kmsg_dump(enum kmsg_dump_reason reason)
 {
+	struct kmsg_dumper_iter iter;
 	struct kmsg_dumper *dumper;
 	unsigned long flags;
 
@@ -3308,25 +3470,21 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 			continue;
 
 		/* initialize iterator with data about the stored records */
-		dumper->active = true;
-
+		iter.active = true;
 		logbuf_lock_irqsave(flags);
-		dumper->cur_seq = clear_seq;
-		dumper->next_seq = prb_next_seq(prb);
+		iter.cur_seq = latched_seq_read_nolock(&clear_seq);
+		iter.next_seq = prb_next_seq(prb);
 		logbuf_unlock_irqrestore(flags);
 
 		/* invoke dumper which will iterate over records */
-		dumper->dump(dumper, reason);
-
-		/* reset iterator */
-		dumper->active = false;
+		dumper->dump(dumper, reason, &iter);
 	}
 	rcu_read_unlock();
 }
 
 /**
  * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dumper iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3343,7 +3501,7 @@ void kmsg_dump(enum kmsg_dump_reason reason)
  *
  * The function is similar to kmsg_dump_get_line(), but grabs no locks.
  */
-bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line_nolock(struct kmsg_dumper_iter *iter, bool syslog,
 			       char *line, size_t size, size_t *len)
 {
 	struct printk_info info;
@@ -3354,16 +3512,16 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 	prb_rec_init_rd(&r, &info, line, size);
 
-	if (!dumper->active)
+	if (!iter->active)
 		goto out;
 
 	/* Read text or count text lines? */
 	if (line) {
-		if (!prb_read_valid(prb, dumper->cur_seq, &r))
+		if (!prb_read_valid(prb, iter->cur_seq, &r))
 			goto out;
 		l = record_print_text(&r, syslog, printk_time);
 	} else {
-		if (!prb_read_valid_info(prb, dumper->cur_seq,
+		if (!prb_read_valid_info(prb, iter->cur_seq,
 					 &info, &line_count)) {
 			goto out;
 		}
@@ -3372,7 +3530,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 	}
 
-	dumper->cur_seq = r.info->seq + 1;
+	iter->cur_seq = r.info->seq + 1;
 	ret = true;
 out:
 	if (len)
@@ -3382,7 +3540,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 /**
  * kmsg_dump_get_line - retrieve one kmsg log line
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dumper iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3397,14 +3555,14 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
  * A return value of FALSE indicates that there are no more records to
  * read.
  */
-bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line(struct kmsg_dumper_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len)
 {
 	unsigned long flags;
 	bool ret;
 
 	logbuf_lock_irqsave(flags);
-	ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);
+	ret = kmsg_dump_get_line_nolock(iter, syslog, line, size, len);
 	logbuf_unlock_irqrestore(flags);
 
 	return ret;
@@ -3413,7 +3571,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
 
 /**
  * kmsg_dump_get_buffer - copy kmsg log lines
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dumper iterator
  * @syslog: include the "<4>" prefixes
  * @buf: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3430,87 +3588,76 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
  * A return value of FALSE indicates that there are no more records to
  * read.
  */
-bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
-			  char *buf, size_t size, size_t *len)
+bool kmsg_dump_get_buffer(struct kmsg_dumper_iter *iter, bool syslog,
+			  char *buf, size_t size, size_t *len_out)
 {
 	struct printk_info info;
-	unsigned int line_count;
 	struct printk_record r;
 	unsigned long flags;
 	u64 seq;
 	u64 next_seq;
-	size_t l = 0;
+	size_t len = 0;
 	bool ret = false;
 	bool time = printk_time;
 
-	prb_rec_init_rd(&r, &info, buf, size);
-
-	if (!dumper->active || !buf || !size)
+	if (!iter->active || !buf || !size)
 		goto out;
 
 	logbuf_lock_irqsave(flags);
-	if (prb_read_valid_info(prb, dumper->cur_seq, &info, NULL)) {
-		if (info.seq != dumper->cur_seq) {
+	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 */
-			dumper->cur_seq = info.seq;
+			iter->cur_seq = info.seq;
 		}
 	}
 
 	/* last entry */
-	if (dumper->cur_seq >= dumper->next_seq) {
+	if (iter->cur_seq >= iter->next_seq) {
 		logbuf_unlock_irqrestore(flags);
 		goto out;
 	}
 
-	/* calculate length of entire buffer */
-	seq = dumper->cur_seq;
-	while (prb_read_valid_info(prb, seq, &info, &line_count)) {
-		if (r.info->seq >= dumper->next_seq)
-			break;
-		l += get_record_print_text_size(&info, line_count, syslog, time);
-		seq = r.info->seq + 1;
-	}
-
-	/* move first record forward until length fits into the buffer */
-	seq = dumper->cur_seq;
-	while (l >= size && prb_read_valid_info(prb, seq,
-						&info, &line_count)) {
-		if (r.info->seq >= dumper->next_seq)
-			break;
-		l -= get_record_print_text_size(&info, line_count, syslog, time);
-		seq = r.info->seq + 1;
-	}
+	/*
+	 * Find first record that fits, including all following records,
+	 * into the user-provided buffer for this dump. Pass in size-1
+	 * because this function (by way of record_print_text()) will
+	 * not write more than size-1 bytes of text into @buf.
+	 */
+	seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
+				     size - 1, syslog, time);
 
-	/* last message in next interation */
+	/*
+	 * Next kmsg_dump_get_buffer() invocation will dump block of
+	 * older records stored right before this one.
+	 */
 	next_seq = seq;
 
-	/* actually read text into the buffer now */
-	l = 0;
-	while (prb_read_valid(prb, seq, &r)) {
-		if (r.info->seq >= dumper->next_seq)
-			break;
+	prb_rec_init_rd(&r, &info, buf, size);
 
-		l += record_print_text(&r, syslog, time);
+	len = 0;
+	prb_for_each_record(seq, prb, seq, &r) {
+		if (r.info->seq >= iter->next_seq)
+			break;
 
-		/* adjust record to store to remaining buffer space */
-		prb_rec_init_rd(&r, &info, buf + l, size - l);
+		len += record_print_text(&r, syslog, time);
 
-		seq = r.info->seq + 1;
+		/* Adjust record to store to remaining buffer space. */
+		prb_rec_init_rd(&r, &info, buf + len, size - len);
 	}
 
-	dumper->next_seq = next_seq;
+	iter->next_seq = next_seq;
 	ret = true;
 	logbuf_unlock_irqrestore(flags);
 out:
-	if (len)
-		*len = l;
+	if (len_out)
+		*len_out = len;
 	return ret;
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
 
 /**
  * kmsg_dump_rewind_nolock - reset the iterator (unlocked version)
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dumper iterator
  *
  * Reset the dumper's iterator so that kmsg_dump_get_line() and
  * kmsg_dump_get_buffer() can be called again and used multiple
@@ -3518,26 +3665,26 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
  *
  * The function is similar to kmsg_dump_rewind(), but grabs no locks.
  */
-void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
+void kmsg_dump_rewind_nolock(struct kmsg_dumper_iter *iter)
 {
-	dumper->cur_seq = clear_seq;
-	dumper->next_seq = prb_next_seq(prb);
+	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
+	iter->next_seq = prb_next_seq(prb);
 }
 
 /**
  * kmsg_dump_rewind - reset the iterator
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dumper iterator
  *
  * Reset the dumper's iterator so that kmsg_dump_get_line() and
  * kmsg_dump_get_buffer() can be called again and used multiple
  * times within the same dumper.dump() callback.
  */
-void kmsg_dump_rewind(struct kmsg_dumper *dumper)
+void kmsg_dump_rewind(struct kmsg_dumper_iter *iter)
 {
 	unsigned long flags;
 
 	logbuf_lock_irqsave(flags);
-	kmsg_dump_rewind_nolock(dumper);
+	kmsg_dump_rewind_nolock(iter);
 	logbuf_unlock_irqrestore(flags);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);