Q: semaphore and kmalloc(GFP_KERNEL)?

[Tetsuo Handa]

Hello.
I got a question.

When we use kmalloc(GFP_KERNEL), we cannot use spinlock.
We use semaphore instead.

What happens if a writer process got into sleep state at kmalloc()
without releasing a rw_semaphore for writing,

    down_write(&sem);
    list_for_each()
        ...;
    ptr = kmalloc(size, GFP_KERNEL);
    list_add();
    up_write(&sem);

and then reader processes tried to hold that rw_semaphore?

    down_read(&sem);
    list_for_each()
        ...;
    up_read(&sem);

Can the kernel detect that we need to let kmalloc() fail and
wake up the writer process so that the writer process releases
the rw_semaphore and reader processes can continue?

(If the kernel can't detect, I worry that we experience
all processes sleeping for undefined duration.)

Regards.
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