kdb: Avoid printing KERN_ levels to consoles

Currently when kdb traps printk messages then the raw log level prefix
(consisting of '\001' followed by a numeral) does not get stripped off
before the message is issued to the various I/O handlers supported by
kdb. This causes annoying visual noise as well as causing problems
grepping for ^. It is also a change of behaviour compared to normal usage
of printk() usage. For example <SysRq>-h ends up with different output to
that of kdb's "sr h".

This patch addresses the problem by stripping log levels from messages
before they are issued to the I/O handlers. printk() which can also
act as an i/o handler in some cases is special cased; if the caller
provided a log level then the prefix will be preserved when sent to
printk().

The addition of non-printable characters to the output of kdb commands is a
regression, albeit and extremely elderly one, introduced by commit
04d2c8c83d0e ("printk: convert the format for KERN_<LEVEL> to a 2 byte
pattern"). Note also that this patch does *not* restore the original
behaviour from v3.5. Instead it makes printk() from within a kdb command
display the message without any prefix (i.e. like printk() normally does).

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Joe Perches <joe@perches.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

2 files changed, 14 insertions, 10 deletions

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 7c70812caea5..a550afb99ebe 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -548,7 +548,7 @@ static int kdb_search_string(char *searched, char *searchfor)
         return 0;
 }
 
-int vkdb_printf(const char *fmt, va_list ap)
+int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
 {
         int diag;
         int linecount;
@@ -691,19 +691,20 @@ kdb_printit:
          * Write to all consoles.
          */
         retlen = strlen(kdb_buffer);
+        cp = (char *) printk_skip_level(kdb_buffer);
         if (!dbg_kdb_mode && kgdb_connected) {
-                gdbstub_msg_write(kdb_buffer, retlen);
+                gdbstub_msg_write(cp, retlen - (cp - kdb_buffer));
         } else {
                 if (dbg_io_ops && !dbg_io_ops->is_console) {
-                        len = retlen;
-                        cp = kdb_buffer;
+                        len = retlen - (cp - kdb_buffer);
+                        cp2 = cp;
                         while (len--) {
-                                dbg_io_ops->write_char(*cp);
-                                cp++;
+                                dbg_io_ops->write_char(*cp2);
+                                cp2++;
                         }
                 }
                 while (c) {
-                        c->write(c, kdb_buffer, retlen);
+                        c->write(c, cp, retlen - (cp - kdb_buffer));
                         touch_nmi_watchdog();
                         c = c->next;
                 }
@@ -711,7 +712,10 @@ kdb_printit:
         if (logging) {
                 saved_loglevel = console_loglevel;
                 console_loglevel = CONSOLE_LOGLEVEL_SILENT;
-                printk(KERN_INFO "%s", kdb_buffer);
+                if (printk_get_level(kdb_buffer) || src == KDB_MSGSRC_PRINTK)
+                        printk("%s", kdb_buffer);
+                else
+                        pr_info("%s", kdb_buffer);
         }
 
         if (KDB_STATE(PAGER)) {
@@ -844,7 +848,7 @@ int kdb_printf(const char *fmt, ...)
         int r;
 
         va_start(ap, fmt);
-        r = vkdb_printf(fmt, ap);
+        r = vkdb_printf(KDB_MSGSRC_INTERNAL, fmt, ap);
         va_end(ap);
 
         return r;
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 02d6b6d28796..fae29e3ffbf0 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1811,7 +1811,7 @@ int vprintk_default(const char *fmt, va_list args)
 
 #ifdef CONFIG_KGDB_KDB
         if (unlikely(kdb_trap_printk)) {
-                r = vkdb_printf(fmt, args);
+                r = vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
                 return r;
         }
 #endif