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    Subject[PATCH] anti-cross-CPU printk/oops interleaving
    Date

    Hi Linus,

    This patch prevents an oops on one CPU being interleaved char-by-char with
    printks being performed on other CPUs, thus rendering them actually readable
    under those circumstances.

    David


    diff -ur linux-2.5.74/kernel/printk.c linux-2.5.74-auto/kernel/printk.c
    --- linux-2.5.74/kernel/printk.c 2003-07-03 15:37:24.000000000 +0100
    +++ linux-2.5.74-auto/kernel/printk.c 2003-07-03 15:41:15.000000000 +0100
    @@ -378,6 +378,9 @@
    logged_chars++;
    }

    +/* cpu currently holding logbuf_lock */
    +static volatile int printk_cpu = -1;
    +
    /*
    * This is printk. It can be called from any context. We want it to work.
    *
    @@ -400,8 +403,9 @@
    static char printk_buf[1024];
    static int log_level_unknown = 1;

    - if (oops_in_progress) {
    - /* If a crash is occurring, make sure we can't deadlock */
    + if (oops_in_progress && printk_cpu == smp_processor_id()) {
    + /* If a crash is occurring during printk() on this CPU,
    + * make sure we can't deadlock */
    spin_lock_init(&logbuf_lock);
    /* And make sure that we print immediately */
    init_MUTEX(&console_sem);
    @@ -409,6 +413,7 @@

    /* This stops the holder of console_sem just where we want him */
    spin_lock_irqsave(&logbuf_lock, flags);
    + printk_cpu = smp_processor_id();

    /* Emit the output into the temporary buffer */
    va_start(args, fmt);
    -
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