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