CODEWITHSUNDEEP
clinux-kernelsignals
ila
ila

Reputation: 58

signal user application from kernel

I have been pulling my hairs for real strange issue. The kernel module is unable to send signal to user application (or user app is unable to receive) without printk, have to do dummy printk after or before sending the signal.

Actually, it works great even with empty printk. But, i am trying to understand whats happening.

Any thoughts?

Here is whats happening:

A - kernel) Char device type module gets interrupt.

It extracts the data and send signal to user.

/* have to do printk here */

Return IRQ handle.

B- user)

Receives the signal.

issues a system call and read the data from char device's buffer . (copy_to_user)

kernel:

void irq_handler(){
    int i;
    for(i =0; i < 32; i++) 
        GPIOdata[i] = read_gpio_status(i);

    struct task_struct *p = find_task_by_pid(processinfo.pid);
    if (NULL == p) 
        return;
    send_sig(SIGUSR1, p, 0);
    /* have to add printk here */
    return IRQ_HANDLED
}

user:

void signal_handler(int sig) {
    char data[32];
    ioctl(fd, READ_Data_from_Char_device, &data);
}

Upvotes: 1

Views: 1384

Answers (1)

zoska
zoska

Reputation: 1723

If you are using signal not sigaction for setting handler, then remember, that signal removes handler after getting a signal. And you should mask the signal, so it will not interrupt your process when running inside signal handler. I'ma also not sure about system call ioctl inside handler (look at man7 signal under section Async-signal-safe functions).

Calls to printk might slow down execution of other operations (because they are blocked on I/O or buffering) around these calls, so they can make synchronization slower (thus any mistakes in synchronization may not occur).

Upvotes: 0

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