kmsg - do not flush partial lines when the console is busy
[cascardo/linux.git] / kernel / printk.c
index a2276b9..4da2377 100644 (file)
@@ -193,12 +193,21 @@ static int console_may_schedule;
  * separated by ',', and find the message after the ';' character.
  */
 
+enum log_flags {
+       LOG_NOCONS      = 1,    /* already flushed, do not print to console */
+       LOG_NEWLINE     = 2,    /* text ended with a newline */
+       LOG_PREFIX      = 4,    /* text started with a prefix */
+       LOG_CONT        = 8,    /* text is a fragment of a continuation line */
+};
+
 struct log {
        u64 ts_nsec;            /* timestamp in nanoseconds */
        u16 len;                /* length of entire record */
        u16 text_len;           /* length of text buffer */
        u16 dict_len;           /* length of dictionary buffer */
-       u16 level;              /* syslog level + facility */
+       u8 facility;            /* syslog facility */
+       u8 flags:5;             /* internal record flags */
+       u8 level:3;             /* syslog level */
 };
 
 /*
@@ -207,9 +216,12 @@ struct log {
  */
 static DEFINE_RAW_SPINLOCK(logbuf_lock);
 
+#ifdef CONFIG_PRINTK
 /* the next printk record to read by syslog(READ) or /proc/kmsg */
 static u64 syslog_seq;
 static u32 syslog_idx;
+static enum log_flags syslog_prev;
+static size_t syslog_partial;
 
 /* index and sequence number of the first record stored in the buffer */
 static u64 log_first_seq;
@@ -217,14 +229,19 @@ static u32 log_first_idx;
 
 /* index and sequence number of the next record to store in the buffer */
 static u64 log_next_seq;
-#ifdef CONFIG_PRINTK
 static u32 log_next_idx;
 
+/* the next printk record to write to the console */
+static u64 console_seq;
+static u32 console_idx;
+static enum log_flags console_prev;
+
 /* the next printk record to read after the last 'clear' command */
 static u64 clear_seq;
 static u32 clear_idx;
 
-#define LOG_LINE_MAX 1024
+#define PREFIX_MAX             32
+#define LOG_LINE_MAX           1024 - PREFIX_MAX
 
 /* record buffer */
 #if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
@@ -286,6 +303,7 @@ static u32 log_next(u32 idx)
 
 /* insert record into the buffer, discard old ones, update heads */
 static void log_store(int facility, int level,
+                     enum log_flags flags, u64 ts_nsec,
                      const char *dict, u16 dict_len,
                      const char *text, u16 text_len)
 {
@@ -329,8 +347,13 @@ static void log_store(int facility, int level,
        msg->text_len = text_len;
        memcpy(log_dict(msg), dict, dict_len);
        msg->dict_len = dict_len;
-       msg->level = (facility << 3) | (level & 7);
-       msg->ts_nsec = local_clock();
+       msg->facility = facility;
+       msg->level = level & 7;
+       msg->flags = flags & 0x1f;
+       if (ts_nsec > 0)
+               msg->ts_nsec = ts_nsec;
+       else
+               msg->ts_nsec = local_clock();
        memset(log_dict(msg) + dict_len, 0, pad_len);
        msg->len = sizeof(struct log) + text_len + dict_len + pad_len;
 
@@ -343,6 +366,7 @@ static void log_store(int facility, int level,
 struct devkmsg_user {
        u64 seq;
        u32 idx;
+       enum log_flags prev;
        struct mutex lock;
        char buf[8192];
 };
@@ -408,6 +432,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
        struct log *msg;
        u64 ts_usec;
        size_t i;
+       char cont = '-';
        size_t len;
        ssize_t ret;
 
@@ -417,20 +442,20 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
        ret = mutex_lock_interruptible(&user->lock);
        if (ret)
                return ret;
-       raw_spin_lock(&logbuf_lock);
+       raw_spin_lock_irq(&logbuf_lock);
        while (user->seq == log_next_seq) {
                if (file->f_flags & O_NONBLOCK) {
                        ret = -EAGAIN;
-                       raw_spin_unlock(&logbuf_lock);
+                       raw_spin_unlock_irq(&logbuf_lock);
                        goto out;
                }
 
-               raw_spin_unlock(&logbuf_lock);
+               raw_spin_unlock_irq(&logbuf_lock);
                ret = wait_event_interruptible(log_wait,
                                               user->seq != log_next_seq);
                if (ret)
                        goto out;
-               raw_spin_lock(&logbuf_lock);
+               raw_spin_lock_irq(&logbuf_lock);
        }
 
        if (user->seq < log_first_seq) {
@@ -438,21 +463,38 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
                user->idx = log_first_idx;
                user->seq = log_first_seq;
                ret = -EPIPE;
-               raw_spin_unlock(&logbuf_lock);
+               raw_spin_unlock_irq(&logbuf_lock);
                goto out;
        }
 
        msg = log_from_idx(user->idx);
        ts_usec = msg->ts_nsec;
        do_div(ts_usec, 1000);
-       len = sprintf(user->buf, "%u,%llu,%llu;",
-                     msg->level, user->seq, ts_usec);
+
+       /*
+        * If we couldn't merge continuation line fragments during the print,
+        * export the stored flags to allow an optional external merge of the
+        * records. Merging the records isn't always neccessarily correct, like
+        * when we hit a race during printing. In most cases though, it produces
+        * better readable output. 'c' in the record flags mark the first
+        * fragment of a line, '+' the following.
+        */
+       if (msg->flags & LOG_CONT && !(user->prev & LOG_CONT))
+               cont = 'c';
+       else if ((msg->flags & LOG_CONT) ||
+                ((user->prev & LOG_CONT) && !(msg->flags & LOG_PREFIX)))
+               cont = '+';
+
+       len = sprintf(user->buf, "%u,%llu,%llu,%c;",
+                     (msg->facility << 3) | msg->level,
+                     user->seq, ts_usec, cont);
+       user->prev = msg->flags;
 
        /* escape non-printable characters */
        for (i = 0; i < msg->text_len; i++) {
                unsigned char c = log_text(msg)[i];
 
-               if (c < ' ' || c >= 128)
+               if (c < ' ' || c >= 127 || c == '\\')
                        len += sprintf(user->buf + len, "\\x%02x", c);
                else
                        user->buf[len++] = c;
@@ -476,7 +518,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
                                continue;
                        }
 
-                       if (c < ' ' || c >= 128) {
+                       if (c < ' ' || c >= 127 || c == '\\') {
                                len += sprintf(user->buf + len, "\\x%02x", c);
                                continue;
                        }
@@ -488,7 +530,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 
        user->idx = log_next(user->idx);
        user->seq++;
-       raw_spin_unlock(&logbuf_lock);
+       raw_spin_unlock_irq(&logbuf_lock);
 
        if (len > count) {
                ret = -EINVAL;
@@ -515,7 +557,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
        if (offset)
                return -ESPIPE;
 
-       raw_spin_lock(&logbuf_lock);
+       raw_spin_lock_irq(&logbuf_lock);
        switch (whence) {
        case SEEK_SET:
                /* the first record */
@@ -539,7 +581,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
        default:
                ret = -EINVAL;
        }
-       raw_spin_unlock(&logbuf_lock);
+       raw_spin_unlock_irq(&logbuf_lock);
        return ret;
 }
 
@@ -553,14 +595,14 @@ static unsigned int devkmsg_poll(struct file *file, poll_table *wait)
 
        poll_wait(file, &log_wait, wait);
 
-       raw_spin_lock(&logbuf_lock);
+       raw_spin_lock_irq(&logbuf_lock);
        if (user->seq < log_next_seq) {
                /* return error when data has vanished underneath us */
                if (user->seq < log_first_seq)
                        ret = POLLIN|POLLRDNORM|POLLERR|POLLPRI;
                ret = POLLIN|POLLRDNORM;
        }
-       raw_spin_unlock(&logbuf_lock);
+       raw_spin_unlock_irq(&logbuf_lock);
 
        return ret;
 }
@@ -584,10 +626,10 @@ static int devkmsg_open(struct inode *inode, struct file *file)
 
        mutex_init(&user->lock);
 
-       raw_spin_lock(&logbuf_lock);
+       raw_spin_lock_irq(&logbuf_lock);
        user->idx = log_first_idx;
        user->seq = log_first_seq;
-       raw_spin_unlock(&logbuf_lock);
+       raw_spin_unlock_irq(&logbuf_lock);
 
        file->private_data = user;
        return 0;
@@ -787,44 +829,64 @@ static bool printk_time;
 #endif
 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 
+static size_t print_time(u64 ts, char *buf)
+{
+       unsigned long rem_nsec;
+
+       if (!printk_time)
+               return 0;
+
+       if (!buf)
+               return 15;
+
+       rem_nsec = do_div(ts, 1000000000);
+       return sprintf(buf, "[%5lu.%06lu] ",
+                      (unsigned long)ts, rem_nsec / 1000);
+}
+
 static size_t print_prefix(const struct log *msg, bool syslog, char *buf)
 {
        size_t len = 0;
+       unsigned int prefix = (msg->facility << 3) | msg->level;
 
        if (syslog) {
                if (buf) {
-                       len += sprintf(buf, "<%u>", msg->level);
+                       len += sprintf(buf, "<%u>", prefix);
                } else {
                        len += 3;
-                       if (msg->level > 9)
-                               len++;
-                       if (msg->level > 99)
+                       if (prefix > 999)
+                               len += 3;
+                       else if (prefix > 99)
+                               len += 2;
+                       else if (prefix > 9)
                                len++;
                }
        }
 
-       if (printk_time) {
-               if (buf) {
-                       unsigned long long ts = msg->ts_nsec;
-                       unsigned long rem_nsec = do_div(ts, 1000000000);
-
-                       len += sprintf(buf + len, "[%5lu.%06lu] ",
-                                        (unsigned long) ts, rem_nsec / 1000);
-               } else {
-                       len += 15;
-               }
-       }
-
+       len += print_time(msg->ts_nsec, buf ? buf + len : NULL);
        return len;
 }
 
-static size_t msg_print_text(const struct log *msg, bool syslog,
-                            char *buf, size_t size)
+static size_t msg_print_text(const struct log *msg, enum log_flags prev,
+                            bool syslog, char *buf, size_t size)
 {
        const char *text = log_text(msg);
        size_t text_size = msg->text_len;
+       bool prefix = true;
+       bool newline = true;
        size_t len = 0;
 
+       if ((prev & LOG_CONT) && !(msg->flags & LOG_PREFIX))
+               prefix = false;
+
+       if (msg->flags & LOG_CONT) {
+               if ((prev & LOG_CONT) && !(prev & LOG_NEWLINE))
+                       prefix = false;
+
+               if (!(msg->flags & LOG_NEWLINE))
+                       newline = false;
+       }
+
        do {
                const char *next = memchr(text, '\n', text_size);
                size_t text_len;
@@ -839,19 +901,25 @@ static size_t msg_print_text(const struct log *msg, bool syslog,
 
                if (buf) {
                        if (print_prefix(msg, syslog, NULL) +
-                           text_len + 1>= size - len)
+                           text_len + 1 >= size - len)
                                break;
 
-                       len += print_prefix(msg, syslog, buf + len);
+                       if (prefix)
+                               len += print_prefix(msg, syslog, buf + len);
                        memcpy(buf + len, text, text_len);
                        len += text_len;
-                       buf[len++] = '\n';
+                       if (next || newline)
+                               buf[len++] = '\n';
                } else {
                        /* SYSLOG_ACTION_* buffer size only calculation */
-                       len += print_prefix(msg, syslog, NULL);
-                       len += text_len + 1;
+                       if (prefix)
+                               len += print_prefix(msg, syslog, NULL);
+                       len += text_len;
+                       if (next || newline)
+                               len++;
                }
 
+               prefix = true;
                text = next;
        } while (text);
 
@@ -862,28 +930,61 @@ static int syslog_print(char __user *buf, int size)
 {
        char *text;
        struct log *msg;
-       int len;
+       int len = 0;
 
-       text = kmalloc(LOG_LINE_MAX, GFP_KERNEL);
+       text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
        if (!text)
                return -ENOMEM;
 
-       raw_spin_lock_irq(&logbuf_lock);
-       if (syslog_seq < log_first_seq) {
-               /* messages are gone, move to first one */
-               syslog_seq = log_first_seq;
-               syslog_idx = log_first_idx;
-       }
-       msg = log_from_idx(syslog_idx);
-       len = msg_print_text(msg, true, text, LOG_LINE_MAX);
-       syslog_idx = log_next(syslog_idx);
-       syslog_seq++;
-       raw_spin_unlock_irq(&logbuf_lock);
+       while (size > 0) {
+               size_t n;
+               size_t skip;
+
+               raw_spin_lock_irq(&logbuf_lock);
+               if (syslog_seq < log_first_seq) {
+                       /* messages are gone, move to first one */
+                       syslog_seq = log_first_seq;
+                       syslog_idx = log_first_idx;
+                       syslog_prev = 0;
+                       syslog_partial = 0;
+               }
+               if (syslog_seq == log_next_seq) {
+                       raw_spin_unlock_irq(&logbuf_lock);
+                       break;
+               }
+
+               skip = syslog_partial;
+               msg = log_from_idx(syslog_idx);
+               n = msg_print_text(msg, syslog_prev, true, text,
+                                  LOG_LINE_MAX + PREFIX_MAX);
+               if (n - syslog_partial <= size) {
+                       /* message fits into buffer, move forward */
+                       syslog_idx = log_next(syslog_idx);
+                       syslog_seq++;
+                       syslog_prev = msg->flags;
+                       n -= syslog_partial;
+                       syslog_partial = 0;
+               } else if (!len){
+                       /* partial read(), remember position */
+                       n = size;
+                       syslog_partial += n;
+               } else
+                       n = 0;
+               raw_spin_unlock_irq(&logbuf_lock);
 
-       if (len > size)
-               len = -EINVAL;
-       else if (len > 0 && copy_to_user(buf, text, len))
-               len = -EFAULT;
+               if (!n)
+                       break;
+
+               if (copy_to_user(buf, text + skip, n)) {
+                       if (!len)
+                               len = -EFAULT;
+                       break;
+               }
+
+               len += n;
+               size -= n;
+               buf += n;
+       }
 
        kfree(text);
        return len;
@@ -894,7 +995,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
        char *text;
        int len = 0;
 
-       text = kmalloc(LOG_LINE_MAX, GFP_KERNEL);
+       text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
        if (!text)
                return -ENOMEM;
 
@@ -903,6 +1004,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
                u64 next_seq;
                u64 seq;
                u32 idx;
+               enum log_flags prev;
 
                if (clear_seq < log_first_seq) {
                        /* messages are gone, move to first available one */
@@ -916,10 +1018,11 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
                 */
                seq = clear_seq;
                idx = clear_idx;
+               prev = 0;
                while (seq < log_next_seq) {
                        struct log *msg = log_from_idx(idx);
 
-                       len += msg_print_text(msg, true, NULL, 0);
+                       len += msg_print_text(msg, prev, true, NULL, 0);
                        idx = log_next(idx);
                        seq++;
                }
@@ -927,10 +1030,11 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
                /* move first record forward until length fits into the buffer */
                seq = clear_seq;
                idx = clear_idx;
+               prev = 0;
                while (len > size && seq < log_next_seq) {
                        struct log *msg = log_from_idx(idx);
 
-                       len -= msg_print_text(msg, true, NULL, 0);
+                       len -= msg_print_text(msg, prev, true, NULL, 0);
                        idx = log_next(idx);
                        seq++;
                }
@@ -939,17 +1043,20 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
                next_seq = log_next_seq;
 
                len = 0;
+               prev = 0;
                while (len >= 0 && seq < next_seq) {
                        struct log *msg = log_from_idx(idx);
                        int textlen;
 
-                       textlen = msg_print_text(msg, true, text, LOG_LINE_MAX);
+                       textlen = msg_print_text(msg, prev, true, text,
+                                                LOG_LINE_MAX + PREFIX_MAX);
                        if (textlen < 0) {
                                len = textlen;
                                break;
                        }
                        idx = log_next(idx);
                        seq++;
+                       prev = msg->flags;
 
                        raw_spin_unlock_irq(&logbuf_lock);
                        if (copy_to_user(buf + len, text, textlen))
@@ -962,6 +1069,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
                                /* messages are gone, move to next one */
                                seq = log_first_seq;
                                idx = log_first_idx;
+                               prev = 0;
                        }
                }
        }
@@ -980,7 +1088,6 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
 {
        bool clear = false;
        static int saved_console_loglevel = -1;
-       static DEFINE_MUTEX(syslog_mutex);
        int error;
 
        error = check_syslog_permissions(type, from_file);
@@ -1007,17 +1114,11 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
                        error = -EFAULT;
                        goto out;
                }
-               error = mutex_lock_interruptible(&syslog_mutex);
-               if (error)
-                       goto out;
                error = wait_event_interruptible(log_wait,
                                                 syslog_seq != log_next_seq);
-               if (error) {
-                       mutex_unlock(&syslog_mutex);
+               if (error)
                        goto out;
-               }
                error = syslog_print(buf, len);
-               mutex_unlock(&syslog_mutex);
                break;
        /* Read/clear last kernel messages */
        case SYSLOG_ACTION_READ_CLEAR:
@@ -1040,6 +1141,7 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
        /* Clear ring buffer */
        case SYSLOG_ACTION_CLEAR:
                syslog_print_all(NULL, 0, true);
+               break;
        /* Disable logging to console */
        case SYSLOG_ACTION_CONSOLE_OFF:
                if (saved_console_loglevel == -1)
@@ -1072,6 +1174,8 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
                        /* messages are gone, move to first one */
                        syslog_seq = log_first_seq;
                        syslog_idx = log_first_idx;
+                       syslog_prev = 0;
+                       syslog_partial = 0;
                }
                if (from_file) {
                        /*
@@ -1081,19 +1185,20 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
                         */
                        error = log_next_idx - syslog_idx;
                } else {
-                       u64 seq;
-                       u32 idx;
+                       u64 seq = syslog_seq;
+                       u32 idx = syslog_idx;
+                       enum log_flags prev = syslog_prev;
 
                        error = 0;
-                       seq = syslog_seq;
-                       idx = syslog_idx;
                        while (seq < log_next_seq) {
                                struct log *msg = log_from_idx(idx);
 
-                               error += msg_print_text(msg, true, NULL, 0);
+                               error += msg_print_text(msg, prev, true, NULL, 0);
                                idx = log_next(idx);
                                seq++;
+                               prev = msg->flags;
                        }
+                       error -= syslog_partial;
                }
                raw_spin_unlock_irq(&logbuf_lock);
                break;
@@ -1272,22 +1377,121 @@ static inline void printk_delay(void)
        }
 }
 
+/*
+ * Continuation lines are buffered, and not committed to the record buffer
+ * until the line is complete, or a race forces it. The line fragments
+ * though, are printed immediately to the consoles to ensure everything has
+ * reached the console in case of a kernel crash.
+ */
+static struct cont {
+       char buf[LOG_LINE_MAX];
+       size_t len;                     /* length == 0 means unused buffer */
+       size_t cons;                    /* bytes written to console */
+       struct task_struct *owner;      /* task of first print*/
+       u64 ts_nsec;                    /* time of first print */
+       u8 level;                       /* log level of first message */
+       u8 facility;                    /* log level of first message */
+       enum log_flags flags;           /* prefix, newline flags */
+       bool flushed:1;                 /* buffer sealed and committed */
+} cont;
+
+static void cont_flush(enum log_flags flags)
+{
+       if (cont.flushed)
+               return;
+       if (cont.len == 0)
+               return;
+
+       if (cont.cons) {
+               /*
+                * If a fragment of this line was directly flushed to the
+                * console; wait for the console to pick up the rest of the
+                * line. LOG_NOCONS suppresses a duplicated output.
+                */
+               log_store(cont.facility, cont.level, flags | LOG_NOCONS,
+                         cont.ts_nsec, NULL, 0, cont.buf, cont.len);
+               cont.flags = flags;
+               cont.flushed = true;
+       } else {
+               /*
+                * If no fragment of this line ever reached the console,
+                * just submit it to the store and free the buffer.
+                */
+               log_store(cont.facility, cont.level, flags, 0,
+                         NULL, 0, cont.buf, cont.len);
+               cont.len = 0;
+       }
+}
+
+static bool cont_add(int facility, int level, const char *text, size_t len)
+{
+       if (cont.len && cont.flushed)
+               return false;
+
+       if (cont.len + len > sizeof(cont.buf)) {
+               /* the line gets too long, split it up in separate records */
+               cont_flush(LOG_CONT);
+               return false;
+       }
+
+       if (!cont.len) {
+               cont.facility = facility;
+               cont.level = level;
+               cont.owner = current;
+               cont.ts_nsec = local_clock();
+               cont.flags = 0;
+               cont.cons = 0;
+               cont.flushed = false;
+       }
+
+       memcpy(cont.buf + cont.len, text, len);
+       cont.len += len;
+
+       if (cont.len > (sizeof(cont.buf) * 80) / 100)
+               cont_flush(LOG_CONT);
+
+       return true;
+}
+
+static size_t cont_print_text(char *text, size_t size)
+{
+       size_t textlen = 0;
+       size_t len;
+
+       if (cont.cons == 0 && (console_prev & LOG_NEWLINE)) {
+               textlen += print_time(cont.ts_nsec, text);
+               size -= textlen;
+       }
+
+       len = cont.len - cont.cons;
+       if (len > 0) {
+               if (len+1 > size)
+                       len = size-1;
+               memcpy(text + textlen, cont.buf + cont.cons, len);
+               textlen += len;
+               cont.cons = cont.len;
+       }
+
+       if (cont.flushed) {
+               if (cont.flags & LOG_NEWLINE)
+                       text[textlen++] = '\n';
+               /* got everything, release buffer */
+               cont.len = 0;
+       }
+       return textlen;
+}
+
 asmlinkage int vprintk_emit(int facility, int level,
                            const char *dict, size_t dictlen,
                            const char *fmt, va_list args)
 {
        static int recursion_bug;
-       static char cont_buf[LOG_LINE_MAX];
-       static size_t cont_len;
-       static int cont_level;
-       static struct task_struct *cont_task;
        static char textbuf[LOG_LINE_MAX];
        char *text = textbuf;
        size_t text_len;
+       enum log_flags lflags = 0;
        unsigned long flags;
        int this_cpu;
-       bool newline = false;
-       bool prefix = false;
        int printed_len = 0;
 
        boot_delay_msec();
@@ -1326,7 +1530,8 @@ asmlinkage int vprintk_emit(int facility, int level,
                recursion_bug = 0;
                printed_len += strlen(recursion_msg);
                /* emit KERN_CRIT message */
-               log_store(0, 2, NULL, 0, recursion_msg, printed_len);
+               log_store(0, 2, LOG_PREFIX|LOG_NEWLINE, 0,
+                         NULL, 0, recursion_msg, printed_len);
        }
 
        /*
@@ -1338,7 +1543,7 @@ asmlinkage int vprintk_emit(int facility, int level,
        /* mark and strip a trailing newline */
        if (text_len && text[text_len-1] == '\n') {
                text_len--;
-               newline = true;
+               lflags |= LOG_NEWLINE;
        }
 
        /* strip syslog prefix and extract log level or control flags */
@@ -1348,7 +1553,7 @@ asmlinkage int vprintk_emit(int facility, int level,
                        if (level == -1)
                                level = text[1] - '0';
                case 'd':       /* KERN_DEFAULT */
-                       prefix = true;
+                       lflags |= LOG_PREFIX;
                case 'c':       /* KERN_CONT */
                        text += 3;
                        text_len -= 3;
@@ -1358,61 +1563,41 @@ asmlinkage int vprintk_emit(int facility, int level,
        if (level == -1)
                level = default_message_loglevel;
 
-       if (dict) {
-               prefix = true;
-               newline = true;
-       }
+       if (dict)
+               lflags |= LOG_PREFIX|LOG_NEWLINE;
 
-       if (!newline) {
-               if (cont_len && (prefix || cont_task != current)) {
-                       /*
-                        * Flush earlier buffer, which is either from a
-                        * different thread, or when we got a new prefix.
-                        */
-                       log_store(facility, cont_level, NULL, 0, cont_buf, cont_len);
-                       cont_len = 0;
-               }
-
-               if (!cont_len) {
-                       cont_level = level;
-                       cont_task = current;
-               }
+       if (!(lflags & LOG_NEWLINE)) {
+               /*
+                * Flush the conflicting buffer. An earlier newline was missing,
+                * or another task also prints continuation lines.
+                */
+               if (cont.len && (lflags & LOG_PREFIX || cont.owner != current))
+                       cont_flush(LOG_NEWLINE);
 
-               /* buffer or append to earlier buffer from the same thread */
-               if (cont_len + text_len > sizeof(cont_buf))
-                       text_len = sizeof(cont_buf) - cont_len;
-               memcpy(cont_buf + cont_len, text, text_len);
-               cont_len += text_len;
+               /* buffer line if possible, otherwise store it right away */
+               if (!cont_add(facility, level, text, text_len))
+                       log_store(facility, level, lflags | LOG_CONT, 0,
+                                 dict, dictlen, text, text_len);
        } else {
-               if (cont_len && cont_task == current) {
-                       if (prefix) {
-                               /*
-                                * New prefix from the same thread; flush. We
-                                * either got no earlier newline, or we race
-                                * with an interrupt.
-                                */
-                               log_store(facility, cont_level,
-                                         NULL, 0, cont_buf, cont_len);
-                               cont_len = 0;
-                       }
+               bool stored = false;
 
-                       /* append to the earlier buffer and flush */
-                       if (cont_len + text_len > sizeof(cont_buf))
-                               text_len = sizeof(cont_buf) - cont_len;
-                       memcpy(cont_buf + cont_len, text, text_len);
-                       cont_len += text_len;
-                       log_store(facility, cont_level,
-                                 NULL, 0, cont_buf, cont_len);
-                       cont_len = 0;
-                       cont_task = NULL;
-                       printed_len = cont_len;
-               } else {
-                       /* ordinary single and terminated line */
-                       log_store(facility, level,
-                                 dict, dictlen, text, text_len);
-                       printed_len = text_len;
+               /*
+                * If an earlier newline was missing and it was the same task,
+                * either merge it with the current buffer and flush, or if
+                * there was a race with interrupts (prefix == true) then just
+                * flush it out and store this line separately.
+                */
+               if (cont.len && cont.owner == current) {
+                       if (!(lflags & LOG_PREFIX))
+                               stored = cont_add(facility, level, text, text_len);
+                       cont_flush(LOG_NEWLINE);
                }
+
+               if (!stored)
+                       log_store(facility, level, lflags, 0,
+                                 dict, dictlen, text, text_len);
        }
+       printed_len += text_len;
 
        /*
         * Try to acquire and then immediately release the console semaphore.
@@ -1496,14 +1681,32 @@ asmlinkage int printk(const char *fmt, ...)
 }
 EXPORT_SYMBOL(printk);
 
-#else
+#else /* CONFIG_PRINTK */
 
+#define LOG_LINE_MAX           0
+#define PREFIX_MAX             0
 #define LOG_LINE_MAX 0
+static u64 syslog_seq;
+static u32 syslog_idx;
+static u64 console_seq;
+static u32 console_idx;
+static enum log_flags syslog_prev;
+static u64 log_first_seq;
+static u32 log_first_idx;
+static u64 log_next_seq;
+static enum log_flags console_prev;
+static struct cont {
+       size_t len;
+       size_t cons;
+       u8 level;
+       bool flushed:1;
+} cont;
 static struct log *log_from_idx(u32 idx) { return NULL; }
 static u32 log_next(u32 idx) { return 0; }
 static void call_console_drivers(int level, const char *text, size_t len) {}
-static size_t msg_print_text(const struct log *msg, bool syslog,
-                            char *buf, size_t size) { return 0; }
+static size_t msg_print_text(const struct log *msg, enum log_flags prev,
+                            bool syslog, char *buf, size_t size) { return 0; }
+static size_t cont_print_text(char *text, size_t size) { return 0; }
 
 #endif /* CONFIG_PRINTK */
 
@@ -1775,9 +1978,34 @@ void wake_up_klogd(void)
                this_cpu_or(printk_pending, PRINTK_PENDING_WAKEUP);
 }
 
-/* the next printk record to write to the console */
-static u64 console_seq;
-static u32 console_idx;
+static void console_cont_flush(char *text, size_t size)
+{
+       unsigned long flags;
+       size_t len;
+
+       raw_spin_lock_irqsave(&logbuf_lock, flags);
+
+       if (!cont.len)
+               goto out;
+
+       /*
+        * We still queue earlier records, likely because the console was
+        * busy. The earlier ones need to be printed before this one, we
+        * did not flush any fragment so far, so just let it queue up.
+        */
+       if (console_seq < log_next_seq && !cont.cons)
+               goto out;
+
+       len = cont_print_text(text, size);
+       raw_spin_unlock(&logbuf_lock);
+       stop_critical_timings();
+       call_console_drivers(cont.level, text, len);
+       start_critical_timings();
+       local_irq_restore(flags);
+       return;
+out:
+       raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+}
 
 /**
  * console_unlock - unlock the console system
@@ -1795,6 +2023,7 @@ static u32 console_idx;
  */
 void console_unlock(void)
 {
+       static char text[LOG_LINE_MAX + PREFIX_MAX];
        static u64 seen_seq;
        unsigned long flags;
        bool wake_klogd = false;
@@ -1807,10 +2036,11 @@ void console_unlock(void)
 
        console_may_schedule = 0;
 
+       /* flush buffered message fragment immediately to console */
+       console_cont_flush(text, sizeof(text));
 again:
        for (;;) {
                struct log *msg;
-               static char text[LOG_LINE_MAX];
                size_t len;
                int level;
 
@@ -1824,18 +2054,36 @@ again:
                        /* messages are gone, move to first one */
                        console_seq = log_first_seq;
                        console_idx = log_first_idx;
+                       console_prev = 0;
                }
-
+skip:
                if (console_seq == log_next_seq)
                        break;
 
                msg = log_from_idx(console_idx);
-               level = msg->level & 7;
-
-               len = msg_print_text(msg, false, text, sizeof(text));
+               if (msg->flags & LOG_NOCONS) {
+                       /*
+                        * Skip record we have buffered and already printed
+                        * directly to the console when we received it.
+                        */
+                       console_idx = log_next(console_idx);
+                       console_seq++;
+                       /*
+                        * We will get here again when we register a new
+                        * CON_PRINTBUFFER console. Clear the flag so we
+                        * will properly dump everything later.
+                        */
+                       msg->flags &= ~LOG_NOCONS;
+                       console_prev = msg->flags;
+                       goto skip;
+               }
 
+               level = msg->level;
+               len = msg_print_text(msg, console_prev, false,
+                                    text, sizeof(text));
                console_idx = log_next(console_idx);
                console_seq++;
+               console_prev = msg->flags;
                raw_spin_unlock(&logbuf_lock);
 
                stop_critical_timings();        /* don't trace print latency */
@@ -2098,6 +2346,7 @@ void register_console(struct console *newcon)
                raw_spin_lock_irqsave(&logbuf_lock, flags);
                console_seq = syslog_seq;
                console_idx = syslog_idx;
+               console_prev = syslog_prev;
                raw_spin_unlock_irqrestore(&logbuf_lock, flags);
                /*
                 * We're about to replay the log buffer.  Only do this to the
@@ -2391,8 +2640,7 @@ bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
        }
 
        msg = log_from_idx(dumper->cur_idx);
-       l = msg_print_text(msg, syslog,
-                             line, size);
+       l = msg_print_text(msg, 0, syslog, line, size);
 
        dumper->cur_idx = log_next(dumper->cur_idx);
        dumper->cur_seq++;
@@ -2409,7 +2657,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
  * kmsg_dump_get_buffer - copy kmsg log lines
  * @dumper: registered kmsg dumper
  * @syslog: include the "<4>" prefixes
- * @line: buffer to copy the line to
+ * @buf: buffer to copy the line to
  * @size: maximum size of the buffer
  * @len: length of line placed into buffer
  *
@@ -2432,6 +2680,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
        u32 idx;
        u64 next_seq;
        u32 next_idx;
+       enum log_flags prev;
        size_t l = 0;
        bool ret = false;
 
@@ -2454,23 +2703,27 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
        /* calculate length of entire buffer */
        seq = dumper->cur_seq;
        idx = dumper->cur_idx;
+       prev = 0;
        while (seq < dumper->next_seq) {
                struct log *msg = log_from_idx(idx);
 
-               l += msg_print_text(msg, true, NULL, 0);
+               l += msg_print_text(msg, prev, true, NULL, 0);
                idx = log_next(idx);
                seq++;
+               prev = msg->flags;
        }
 
        /* move first record forward until length fits into the buffer */
        seq = dumper->cur_seq;
        idx = dumper->cur_idx;
+       prev = 0;
        while (l > size && seq < dumper->next_seq) {
                struct log *msg = log_from_idx(idx);
 
-               l -= msg_print_text(msg, true, NULL, 0);
+               l -= msg_print_text(msg, prev, true, NULL, 0);
                idx = log_next(idx);
                seq++;
+               prev = msg->flags;
        }
 
        /* last message in next interation */
@@ -2478,14 +2731,14 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
        next_idx = idx;
 
        l = 0;
+       prev = 0;
        while (seq < dumper->next_seq) {
                struct log *msg = log_from_idx(idx);
 
-               l += msg_print_text(msg, syslog,
-                                   buf + l, size - l);
-
+               l += msg_print_text(msg, prev, syslog, buf + l, size - l);
                idx = log_next(idx);
                seq++;
+               prev = msg->flags;
        }
 
        dumper->next_seq = next_seq;