[PATCH v2 3.18-rc3] kdb: Avoid printing KERN_ levels to consoles

[Daniel Thompson]

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 this 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@xxxxxxxxxx>
Cc: Jason Wessel <jason.wessel@xxxxxxxxxxxxx>
Cc: Joe Perches <joe@xxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---

Notes:
    This patch is tested both on arm (kgdboc=ttyAMA0) and x86_64
    (kgdboc=kdb,ttyS0).
    
    v2:
    
    * Adopt printk_skip_level() to skip the header characters (Joe Perches).
    
    * Update patch description to describe the addition of non-printable
      characters to kdb output as a regression and Cc: stable@ (Joe Perches).
    

 kernel/debug/kdb/kdb_io.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 7c70812caea5..f3982adf8695 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -691,19 +691,20 @@ kdb_printit:
 	 * Write to all consoles.
 	 */
 	retlen = strlen(kdb_buffer);
+	cp = 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 (cp == kdb_buffer)
+			printk(KERN_INFO "%s", kdb_buffer);
+		else
+			printk("%s", kdb_buffer);
 	}

 	if (KDB_STATE(PAGER)) {
--
1.9.3

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