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%3Ba=su...

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 stable@vger.kernel.org know about it.

From foo@baz Sun Mar 18 16:55:33 CET 2018

From: Pan Xinhui xinhui.pan@linux.vnet.ibm.com Date: Wed, 22 Mar 2017 16:27:49 -0300 Subject: powerpc/xmon: Fix an unexpected xmon on/off state change

From: Pan Xinhui xinhui.pan@linux.vnet.ibm.com

[ 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.

Signed-off-by: Pan Xinhui xinhui.pan@linux.vnet.ibm.com Signed-off-by: Guilherme G. Piccoli gpiccoli@linux.vnet.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/xmon/xmon.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-)

--- a/arch/powerpc/xmon/xmon.c +++ b/arch/powerpc/xmon/xmon.c @@ -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 xinhui.pan@linux.vnet.ibm.com are

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