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    SubjectRe: [PATCH -mm v4 6/9] atmel_serial: Split the interrupt handler
    On Wed, 30 Jan 2008 00:12:23 +0100
    michael <trimarchi@gandalf.sssup.it> wrote:

    > I'm testing this patch on an at91sam9260 on 2.6.24-rt. I'm using this
    > patch with the tclib support for hrtimer and the clocksource pit_clk.
    > These are the results:
    >
    > - Voluntary Kernel Preemption the system (crash)
    > - Preemptible Kernel (crash)

    Ouch. I'm assuming this is with DMA disabled?

    > /*
    > * Drop the lock here since it might end up calling
    > * uart_start(), which takes the lock.
    > spin_unlock(&port->lock);
    > */
    > tty_flip_buffer_push(port->info->tty);
    > /*
    > spin_lock(&port->lock);
    > */
    > The same code with this comments out runs

    Now, _that_ is strange. I can't see anything that needs protection
    across that call; in fact, I think we can lock a lot less than what we
    currently do.

    > Complete Preemption (Real-Time) ok but the serials is just unusable due
    > to too many overruns (just using lrz)

    Is it worse than before? IIRC Remy mentioned something about
    IRQF_NODELAY being the reason for moving all this code to softirq
    context in the first place; does the interrupt handler run in hardirq
    context?

    > The system is stable and doesn't crash reverting this patch.
    > I don't test with the thread hardirqs active.

    Ok.

    > >> + ret = -ENOMEM;
    > >> + data = kmalloc(ATMEL_SERIAL_RINGSIZE, GFP_KERNEL);
    > >> + if (!data)
    > >> + goto err_alloc_ring;
    > >> + port->rx_ring.buf = data;
    > >> +
    > >> ret = uart_add_one_port(&atmel_uart, &port->uart);
    > >>
    > Is the kmalloc correct?
    > maybe:
    > data = kmalloc(ATMEL_SERIAL_RINGSIZE * sizeof(struct atmel_uart_char),
    > GFP_KERNEL);

    I think you're right. Can you change it and see if it helps?

    I guess I didn't test it thoroughly enough with DMA
    disabled...slub_debug ought to catch such things, but not until we
    receive enough data to actually overflow the buffer.

    > >> @@ -1033,6 +1165,9 @@ static int __devexit atmel_serial_remove(struct platform_device *pdev)
    > >>
    > >> ret = uart_remove_one_port(&atmel_uart, port);
    > >>
    > >> + tasklet_kill(&atmel_port->tasklet);
    > >> + kfree(atmel_port->rx_ring.buf);
    > >> +
    > >>
    > Why the tasklet_kill is not done in atmel_shutdown?

    Why should it be? If it should, we must move the call to tasklet_init
    into atmel_startup too, and I don't really see the point.

    Haavard


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