Patch "powerpc/xmon: Fix an unexpected xmon on/off state change" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

powerpc/xmon: Fix an unexpected xmon on/off state change

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
powerpc-xmon-fix-an-unexpected-xmon-on-off-state-change.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Pan Xinhui <[email protected]>
Date: Wed, 22 Mar 2017 16:27:49 -0300
Subject: powerpc/xmon: Fix an unexpected xmon on/off state change

From: Pan Xinhui <[email protected]>

[ Upstream commit 3b5bf42b81d56085fd58692b5117f69aa77fdff7 ]

Once xmon is triggered by sysrq-x, it is enabled always afterwards even if it is disabled during boot. This will cause a system reset interrupt fail to dump. So keep xmon in its original state after exit.

We have several ways to set xmon on or off.
1) by a build config CONFIG_XMON_DEFAULT.
2) by a boot cmdline with xmon or xmon=early or xmon=on to enable xmon and xmon=off to disable xmon. This value will override that in step 1.
3) by a debugfs interface, as proposed in this patchset. And this value can override those in step 1 and 2.

---
 arch/powerpc/xmon/xmon.c |   17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

@@ -74,6 +74,7 @@ static int xmon_gate;
 #endif /* CONFIG_SMP */
 
 static unsigned long in_xmon __read_mostly = 0;
+static int xmon_on = IS_ENABLED(CONFIG_XMON_DEFAULT);
 
 static unsigned long adrs;
 static int size = 1;

@@ -3244,6 +3245,8 @@ static void sysrq_handle_xmon(int key)
 	/* ensure xmon is enabled */
 	xmon_init(1);
 	debugger(get_irq_regs());
+	if (!xmon_on)
+		xmon_init(0);
 }
 
 static struct sysrq_key_op sysrq_xmon_op = {

@@ -3260,7 +3263,7 @@ static int __init setup_xmon_sysrq(void)
 __initcall(setup_xmon_sysrq);
 #endif /* CONFIG_MAGIC_SYSRQ */
 
-static int __initdata xmon_early, xmon_off;
+static int __initdata xmon_early;
 
 static int __init early_parse_xmon(char *p)
 {

@@ -3268,10 +3271,12 @@ static int __init early_parse_xmon(char
 		/* just "xmon" is equivalent to "xmon=early" */
 		xmon_init(1);
 		xmon_early = 1;
-	} else if (strncmp(p, "on", 2) == 0)
+		xmon_on = 1;
+	} else if (strncmp(p, "on", 2) == 0) {
 		xmon_init(1);
-	else if (strncmp(p, "off", 3) == 0)
-		xmon_off = 1;
+		xmon_on = 1;
+	} else if (strncmp(p, "off", 3) == 0)
+		xmon_on = 0;
 	else if (strncmp(p, "nobt", 4) == 0)
 		xmon_no_auto_backtrace = 1;
 	else

@@ -3283,10 +3288,8 @@ early_param("xmon", early_parse_xmon);
 
 void __init xmon_setup(void)
 {
-#ifdef CONFIG_XMON_DEFAULT
-	if (!xmon_off)
+	if (xmon_on)
 		xmon_init(1);
-#endif
 	if (xmon_early)
 		debugger(NULL);
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/powerpc-xmon-fix-an-unexpected-xmon-on-off-state-change.patch

Please drop this from stable for now, there are some fixes for it pending in my next branch.

cheers

Now dropped, thanks for letting me know.

greg k-h