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    Subject[RFC][PATCHv5 07/13] printk: register syscore notifier
    Date
    We need to switch to emergency printk mode in kernel_kexec(). One
    kernel_kexec() branch calls kernel_restart_prepare(), which updates
    `system_state', however, the other one, when user requested to
    ->preserve_context, does not and we are lacking the information
    in printk about kexec being executed. Register a syscore notifier
    so printk will be notified by syscore_suspend().

    Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
    ---
    kernel/printk/printk.c | 19 +++++++++++++++++++
    1 file changed, 19 insertions(+)

    diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
    index d3f149fad85c..b14e35f94596 100644
    --- a/kernel/printk/printk.c
    +++ b/kernel/printk/printk.c
    @@ -50,6 +50,7 @@
    #include <linux/sched/task_stack.h>
    #include <linux/kthread.h>
    #include <linux/suspend.h>
    +#include <linux/syscore_ops.h>

    #include <linux/uaccess.h>
    #include <asm/sections.h>
    @@ -2941,6 +2942,22 @@ static struct notifier_block printk_pm_nb = {
    .notifier_call = printk_pm_notify,
    };

    +static int printk_syscore_suspend(void)
    +{
    + printk_emergency_begin();
    + return 0;
    +}
    +
    +static void printk_syscore_resume(void)
    +{
    + printk_emergency_end();
    +}
    +
    +static struct syscore_ops printk_syscore_ops = {
    + .suspend = printk_syscore_suspend,
    + .resume = printk_syscore_resume,
    +};
    +
    static int printk_kthread_func(void *data)
    {
    while (1) {
    @@ -2994,6 +3011,8 @@ static int __init init_printk_kthread(void)
    return -EINVAL;
    }

    + register_syscore_ops(&printk_syscore_ops);
    +
    thread = kthread_run(printk_kthread_func, NULL, "printk");
    if (IS_ERR(thread)) {
    pr_err("printk: unable to create printing thread\n");
    --
    2.14.1
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