[PATCH AUTOSEL for 4.9 073/219] powerpc/xmon: Fix an unexpected xmon on/off state change

Sasha Levin
2018-03-03T23:53:29Z

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

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 760545519a0b..b975a256e606 100644
--- 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 *p)
/* 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);
}
--
2.14.1