How to print linux workqueue worker's printk immediately into dmesg?

Question

I have a question about linux workqueue. I found example kernel module using workqueue and tested it. Here is the code.

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/workqueue.h>
#include <linux/slab.h>

MODULE_LICENSE( "GPL" );

static struct workqueue_struct *my_wq;

typedef struct {
    struct work_struct my_work;
    int    x;
} my_work_t;

my_work_t *work, *work2;


static void my_wq_function( struct work_struct *work)
{
    my_work_t *my_work = (my_work_t *)work;

    printk( "my_work.x %d", my_work->x );

    kfree( (void *)work );

    return;
}

static int __init init_workqueue( void )
{
    int ret;

    my_wq = create_workqueue("my_queue");
    if (my_wq) {

        /* Queue some work (item 1) */
        work = (my_work_t *)kmalloc(sizeof(my_work_t), GFP_KERNEL);
        if (work) {

            INIT_WORK( (struct work_struct *)work, my_wq_function );

            work->x = 1;

            ret = queue_work( my_wq, (struct work_struct *)work );

        }

        /* Queue some additional work (item 2) */
        work2 = (my_work_t *)kmalloc(sizeof(my_work_t), GFP_KERNEL);
        if (work2) {

            INIT_WORK( (struct work_struct *)work2, my_wq_function );

            work2->x = 2;

            ret = queue_work( my_wq, (struct work_struct *)work2 );

        }

    }

    return 0;
}

static void __exit exit_workqueue( void )
{
    flush_workqueue( my_wq );
    destroy_workqueue( my_wq );

    return;
}

module_init(init_workqueue)
module_exit(exit_workqueue)

And this is result. left shows what I entered and right shows the dmesg. I don't know why work2's printk doesn't show up.

After I reinsert my module, then it appears.

How can I get printk message from queued work?

Answer 1

Your calls to printk() don't end with a newline character (\n) and therefore dmesg does not print anything until the next call adds a new entry in the kernel message buffer.

Just add a newline at the end of your format strings, like this:

printk("my_work.x %d\n", my_work->x);
//                  ^^