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    Subject[PATCH 02/11] kdb: Implement disable_nmi command
    Date
    This command disables NMI-entry. If NMI source has been previously shared
    with a serial console ("debug port"), this effectively releases the port
    from KDB exclusive use, and makes the console available for normal use.

    Of course, NMI can be reenabled, enable_nmi modparam is used for that:

    echo 1 > /sys/module/kdb/parameters/enable_nmi

    Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
    ---
    kernel/debug/kdb/kdb_main.c | 31 +++++++++++++++++++++++++++++++
    1 file changed, 31 insertions(+)

    diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
    index 31df170..1261dc7 100644
    --- a/kernel/debug/kdb/kdb_main.c
    +++ b/kernel/debug/kdb/kdb_main.c
    @@ -21,6 +21,7 @@
    #include <linux/smp.h>
    #include <linux/utsname.h>
    #include <linux/vmalloc.h>
    +#include <linux/atomic.h>
    #include <linux/module.h>
    #include <linux/mm.h>
    #include <linux/init.h>
    @@ -2107,6 +2108,32 @@ static int kdb_dmesg(int argc, const char **argv)
    return 0;
    }
    #endif /* CONFIG_PRINTK */
    +
    +/* Make sure we balance enable/disable calls, must disable first. */
    +static atomic_t kdb_nmi_disabled;
    +
    +static int kdb_disable_nmi(int argc, const char *argv[])
    +{
    + if (atomic_read(&kdb_nmi_disabled))
    + return 0;
    + atomic_set(&kdb_nmi_disabled, 1);
    + arch_kgdb_ops.enable_nmi(0);
    + return 0;
    +}
    +
    +static int kdb_param_enable_nmi(const char *val, const struct kernel_param *kp)
    +{
    + if (!atomic_add_unless(&kdb_nmi_disabled, -1, 0))
    + return -EINVAL;
    + arch_kgdb_ops.enable_nmi(1);
    + return 0;
    +}
    +
    +static const struct kernel_param_ops kdb_param_ops_enable_nmi = {
    + .set = kdb_param_enable_nmi,
    +};
    +module_param_cb(enable_nmi, &kdb_param_ops_enable_nmi, NULL, 0600);
    +
    /*
    * kdb_cpu - This function implements the 'cpu' command.
    * cpu [<cpunum>]
    @@ -2851,6 +2878,10 @@ static void __init kdb_inittab(void)
    kdb_register_repeat("dmesg", kdb_dmesg, "[lines]",
    "Display syslog buffer", 0, KDB_REPEAT_NONE);
    #endif
    + if (arch_kgdb_ops.enable_nmi) {
    + kdb_register_repeat("disable_nmi", kdb_disable_nmi, "",
    + "Disable NMI entry to KDB", 0, KDB_REPEAT_NONE);
    + }
    kdb_register_repeat("defcmd", kdb_defcmd, "name \"usage\" \"help\"",
    "Define a set of commands, down to endefcmd", 0, KDB_REPEAT_NONE);
    kdb_register_repeat("kill", kdb_kill, "<-signal> <pid>",
    --
    1.7.11.5


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