Merge branch 'anton-kgdb' (kgdb dmesg fixups)

Merge emailed kgdb dmesg fixups patches from Anton Vorontsov:
 "The dmesg command appears to be broken after the printk rework.  The
  old logic in the kdb code makes no sense in terms of current
  printk/logging storage format, and KDB simply hangs forever upon
  entering 'dmesg' command.

  The first patch revives the command by switching to kmsg_dumper
  iterator.  As a side-effect, the code is now much more simpler.

  A few changes were needed in the printk.c: we needed unlocked variant
  of the kmsg_dumper iterator, but these can surely wait for 3.6.

  It's probably too late even for the first patch to go to 3.5, but I'll
  try to convince otherwise.  :-) Here we go:

   - The current code is broken for sure, and has no hope to work at
     all.  It is a regression
   - The new code works for me, and probably works for everyone else;
   - If it compiles (and I urge everyone to compile-test it on your
     setup), it hardly can make things worse."

* Merge emailed patches from Anton Vorontsov: (4 commits)
  kdb: Switch to nolock variants of kmsg_dump functions
  printk: Implement some unlocked kmsg_dump functions
  printk: Remove kdb_syslog_data
  kdb: Revive dmesg command

4 files changed, 104 insertions, 87 deletions

diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index d6bd50110ec2..2e7a1e032c71 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -55,12 +55,17 @@ struct kmsg_dumper {
 #ifdef CONFIG_PRINTK
 void kmsg_dump(enum kmsg_dump_reason reason);
 
+bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
+                               char *line, size_t size, size_t *len);
+
 bool kmsg_dump_get_line(struct kmsg_dumper *dumper, 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);
 
+void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper);
+
 void kmsg_dump_rewind(struct kmsg_dumper *dumper);
 
 int kmsg_dump_register(struct kmsg_dumper *dumper);
@@ -71,6 +76,13 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason)
 {
 }
 
+static inline bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper,
+                                             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,
                                 const char *line, size_t size, size_t *len)
 {
@@ -83,6 +95,10 @@ static inline bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
         return false;
 }
 
+static inline void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
+{
+}
+
 static inline void kmsg_dump_rewind(struct kmsg_dumper *dumper)
 {
 }
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 67b847dfa2bb..1f91413edb87 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -14,6 +14,7 @@
 #include <linux/ctype.h>
 #include <linux/string.h>
 #include <linux/kernel.h>
+#include <linux/kmsg_dump.h>
 #include <linux/reboot.h>
 #include <linux/sched.h>
 #include <linux/sysrq.h>
@@ -2040,8 +2041,15 @@ static int kdb_env(int argc, const char **argv)
  */
 static int kdb_dmesg(int argc, const char **argv)
 {
-        char *syslog_data[4], *start, *end, c = '\0', *p;
-        int diag, logging, logsize, lines = 0, adjust = 0, n;
+        int diag;
+        int logging;
+        int lines = 0;
+        int adjust = 0;
+        int n = 0;
+        int skip = 0;
+        struct kmsg_dumper dumper = { .active = 1 };
+        size_t len;
+        char buf[201];
 
         if (argc > 2)
                 return KDB_ARGCOUNT;
@@ -2064,22 +2072,10 @@ static int kdb_dmesg(int argc, const char **argv)
                 kdb_set(2, setargs);
         }
 
-        /* syslog_data[0,1] physical start, end+1.  syslog_data[2,3]
-         * logical start, end+1. */
-        kdb_syslog_data(syslog_data);
-        if (syslog_data[2] == syslog_data[3])
-                return 0;
-        logsize = syslog_data[1] - syslog_data[0];
-        start = syslog_data[2];
-        end = syslog_data[3];
-#define KDB_WRAP(p) (((p - syslog_data[0]) % logsize) + syslog_data[0])
-        for (n = 0, p = start; p < end; ++p) {
-                c = *KDB_WRAP(p);
-                if (c == '\n')
-                        ++n;
-        }
-        if (c != '\n')
-                ++n;
+        kmsg_dump_rewind_nolock(&dumper);
+        while (kmsg_dump_get_line_nolock(&dumper, 1, NULL, 0, NULL))
+                n++;
+
         if (lines < 0) {
                 if (adjust >= n)
                         kdb_printf("buffer only contains %d lines, nothing "
@@ -2087,21 +2083,11 @@ static int kdb_dmesg(int argc, const char **argv)
                 else if (adjust - lines >= n)
                         kdb_printf("buffer only contains %d lines, last %d "
                                    "lines printed\n", n, n - adjust);
-                if (adjust) {
-                        for (; start < end && adjust; ++start) {
-                                if (*KDB_WRAP(start) == '\n')
-                                        --adjust;
-                        }
-                        if (start < end)
-                                ++start;
-                }
-                for (p = start; p < end && lines; ++p) {
-                        if (*KDB_WRAP(p) == '\n')
-                                ++lines;
-                }
-                end = p;
+                skip = adjust;
+                lines = abs(lines);
         } else if (lines > 0) {
-                int skip = n - (adjust + lines);
+                skip = n - lines - adjust;
+                lines = abs(lines);
                 if (adjust >= n) {
                         kdb_printf("buffer only contains %d lines, "
                                    "nothing printed\n", n);
@@ -2112,35 +2098,24 @@ static int kdb_dmesg(int argc, const char **argv)
                         kdb_printf("buffer only contains %d lines, first "
                                    "%d lines printed\n", n, lines);
                 }
-                for (; start < end && skip; ++start) {
-                        if (*KDB_WRAP(start) == '\n')
-                                --skip;
-                }
-                for (p = start; p < end && lines; ++p) {
-                        if (*KDB_WRAP(p) == '\n')
-                                --lines;
-                }
-                end = p;
+        } else {
+                lines = n;
         }
-        /* Do a line at a time (max 200 chars) to reduce protocol overhead */
-        c = '\n';
-        while (start != end) {
-                char buf[201];
-                p = buf;
-                if (KDB_FLAG(CMD_INTERRUPT))
-                        return 0;
-                while (start < end && (c = *KDB_WRAP(start)) &&
-                       (p - buf) < sizeof(buf)-1) {
-                        ++start;
-                        *p++ = c;
-                        if (c == '\n')
-                                break;
+
+        if (skip >= n || skip < 0)
+                return 0;
+
+        kmsg_dump_rewind_nolock(&dumper);
+        while (kmsg_dump_get_line_nolock(&dumper, 1, buf, sizeof(buf), &len)) {
+                if (skip) {
+                        skip--;
+                        continue;
                 }
-                *p = '\0';
-                kdb_printf("%s", buf);
+                if (!lines--)
+                        break;
+
+                kdb_printf("%.*s\n", (int)len - 1, buf);
         }
-        if (c != '\n')
-                kdb_printf("\n");
 
         return 0;
 }
diff --git a/kernel/debug/kdb/kdb_private.h b/kernel/debug/kdb/kdb_private.h
index 47c4e56e513b..392ec6a25844 100644
--- a/kernel/debug/kdb/kdb_private.h
+++ b/kernel/debug/kdb/kdb_private.h
@@ -205,7 +205,6 @@ extern char kdb_grep_string[];
 extern int kdb_grep_leading;
 extern int kdb_grep_trailing;
 extern char *kdb_cmds[];
-extern void kdb_syslog_data(char *syslog_data[]);
 extern unsigned long kdb_task_state_string(const char *);
 extern char kdb_task_state_char (const struct task_struct *);
 extern unsigned long kdb_task_state(const struct task_struct *p,
diff --git a/kernel/printk.c b/kernel/printk.c
index 177fa49357a5..ac4bc9e79465 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -1192,21 +1192,6 @@ SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
         return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
 }
 
-#ifdef  CONFIG_KGDB_KDB
-/* kdb dmesg command needs access to the syslog buffer.  do_syslog()
- * uses locks so it cannot be used during debugging.  Just tell kdb
- * where the start and end of the physical and logical logs are.  This
- * is equivalent to do_syslog(3).
- */
-void kdb_syslog_data(char *syslog_data[4])
-{
-        syslog_data[0] = log_buf;
-        syslog_data[1] = log_buf + log_buf_len;
-        syslog_data[2] = log_buf + log_first_idx;
-        syslog_data[3] = log_buf + log_next_idx;
-}
-#endif  /* CONFIG_KGDB_KDB */
-
 static bool __read_mostly ignore_loglevel;
 
 static int __init ignore_loglevel_setup(char *str)
@@ -2525,7 +2510,7 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 }
 
 /**
- * kmsg_dump_get_line - retrieve one kmsg log line
+ * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
  * @dumper: registered kmsg dumper
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
@@ -2540,11 +2525,12 @@ void kmsg_dump(enum kmsg_dump_reason reason)
  *
  * A return value of FALSE indicates that there are no more records to
  * read.
+ *
+ * The function is similar to kmsg_dump_get_line(), but grabs no locks.
  */
-bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
-                        char *line, size_t size, size_t *len)
+bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
+                               char *line, size_t size, size_t *len)
 {
-        unsigned long flags;
         struct log *msg;
         size_t l = 0;
         bool ret = false;
@@ -2552,7 +2538,6 @@ bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
         if (!dumper->active)
                 goto out;
 
-        raw_spin_lock_irqsave(&logbuf_lock, flags);
         if (dumper->cur_seq < log_first_seq) {
                 /* messages are gone, move to first available one */
                 dumper->cur_seq = log_first_seq;
@@ -2560,10 +2545,8 @@ bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
         }
 
         /* last entry */
-        if (dumper->cur_seq >= log_next_seq) {
-                raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+        if (dumper->cur_seq >= log_next_seq)
                 goto out;
-        }
 
         msg = log_from_idx(dumper->cur_idx);
         l = msg_print_text(msg, 0, syslog, line, size);
@@ -2571,12 +2554,41 @@ bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
         dumper->cur_idx = log_next(dumper->cur_idx);
         dumper->cur_seq++;
         ret = true;
-        raw_spin_unlock_irqrestore(&logbuf_lock, flags);
 out:
         if (len)
                 *len = l;
         return ret;
 }
+
+/**
+ * kmsg_dump_get_line - retrieve one kmsg log line
+ * @dumper: registered kmsg dumper
+ * @syslog: include the "<4>" prefixes
+ * @line: buffer to copy the line to
+ * @size: maximum size of the buffer
+ * @len: length of line placed into buffer
+ *
+ * Start at the beginning of the kmsg buffer, with the oldest kmsg
+ * record, and copy one record into the provided buffer.
+ *
+ * Consecutive calls will return the next available record moving
+ * towards the end of the buffer with the youngest messages.
+ *
+ * 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,
+                        char *line, size_t size, size_t *len)
+{
+        unsigned long flags;
+        bool ret;
+
+        raw_spin_lock_irqsave(&logbuf_lock, flags);
+        ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);
+        raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+
+        return ret;
+}
 EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
 
 /**
@@ -2679,6 +2691,24 @@ out:
 EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
 
 /**
+ * kmsg_dump_rewind_nolock - reset the interator (unlocked version)
+ * @dumper: registered kmsg dumper
+ *
+ * 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.
+ *
+ * The function is similar to kmsg_dump_rewind(), but grabs no locks.
+ */
+void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
+{
+        dumper->cur_seq = clear_seq;
+        dumper->cur_idx = clear_idx;
+        dumper->next_seq = log_next_seq;
+        dumper->next_idx = log_next_idx;
+}
+
+/**
  * kmsg_dump_rewind - reset the interator
  * @dumper: registered kmsg dumper
  *
@@ -2691,10 +2721,7 @@ void kmsg_dump_rewind(struct kmsg_dumper *dumper)
         unsigned long flags;
 
         raw_spin_lock_irqsave(&logbuf_lock, flags);
-        dumper->cur_seq = clear_seq;
-        dumper->cur_idx = clear_idx;
-        dumper->next_seq = log_next_seq;
-        dumper->next_idx = log_next_idx;
+        kmsg_dump_rewind_nolock(dumper);
         raw_spin_unlock_irqrestore(&logbuf_lock, flags);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);