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    SubjectRe: [prepatch] removal of oops->printk deadlocks
    Ingo Molnar wrote:
    >
    > > So... In this updated patch the console_silent() call remains
    > > as you designed it, but the nmi_watchdog kernel boot parameter has
    > > been overloaded so that
    > >
    > > nmi_watchdog=2
    > >
    > > will now cause _all_ NMI oops messages to be displayed on the console.
    > >
    > > Is this OK?
    >
    > this collides with the UP-IOAPIC path's use of nmi_watchdog == 2 ...
    >
    > i'd rather suggest a cleaner, "nmi_watchdog=2,verbose" (default: silent)
    > type of boot parameter, it looks like the NMI watchdog needs more
    > parameters.


    OK, so the options are now:

    nmi_watchdog=0
    nmi_watchdog=1
    nmi_watchdog=1,verbose


    Third time lucky?



    --- linux-2.4.0-test11-pre5/include/linux/kernel.h Sun Oct 15 01:27:46 2000
    +++ linux-akpm/include/linux/kernel.h Wed Nov 15 23:25:48 2000
    @@ -62,6 +62,7 @@

    asmlinkage int printk(const char * fmt, ...)
    __attribute__ ((format (printf, 1, 2)));
    +extern int oops_in_progress;

    #if DEBUG
    #define pr_debug(fmt,arg...) \
    --- linux-2.4.0-test11-pre5/include/asm-i386/page.h Sat Nov 4 16:22:49 2000
    +++ linux-akpm/include/asm-i386/page.h Wed Nov 15 23:27:32 2000
    @@ -88,8 +88,9 @@
    * Tell the user there is some problem. Beep too, so we can
    * see^H^H^Hhear bugs in early bootup as well!
    */
    +extern void do_BUG(const char *file, int line);
    #define BUG() do { \
    - printk("kernel BUG at %s:%d!\n", __FILE__, __LINE__); \
    + do_BUG(__FILE__, __LINE__); \
    __asm__ __volatile__(".byte 0x0f,0x0b"); \
    } while (0)

    --- linux-2.4.0-test11-pre5/kernel/printk.c Sat Nov 4 16:22:49 2000
    +++ linux-akpm/kernel/printk.c Wed Nov 15 23:25:48 2000
    @@ -51,6 +51,7 @@
    static unsigned long logged_chars;
    struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
    static int preferred_console = -1;
    +int oops_in_progress;

    /*
    * Setup a list of consoles. Called from init/main.c
    @@ -251,6 +252,9 @@
    return do_syslog(type, buf, len);
    }

    +/*
    + * printk("") may be used to wake up klogd
    + */
    asmlinkage int printk(const char *fmt, ...)
    {
    va_list args;
    @@ -260,6 +264,8 @@
    static signed char msg_level = -1;
    long flags;

    + if (oops_in_progress)
    + spin_lock_init(&console_lock);
    spin_lock_irqsave(&console_lock, flags);
    va_start(args, fmt);
    i = vsprintf(buf + 3, fmt, args); /* hopefully i < sizeof(buf)-4 */
    @@ -308,7 +314,8 @@
    msg_level = -1;
    }
    spin_unlock_irqrestore(&console_lock, flags);
    - wake_up_interruptible(&log_wait);
    + if (!oops_in_progress)
    + wake_up_interruptible(&log_wait);
    return i;
    }

    --- linux-2.4.0-test11-pre5/arch/i386/mm/fault.c Wed Nov 15 23:00:16 2000
    +++ linux-akpm/arch/i386/mm/fault.c Thu Nov 16 00:14:37 2000
    @@ -77,17 +77,37 @@
    return 0;
    }

    -extern spinlock_t console_lock, timerlist_lock;
    +#ifdef CONFIG_SMP
    +extern unsigned volatile int global_irq_lock;
    +#endif

    /*
    * Unlock any spinlocks which will prevent us from getting the
    - * message out (timerlist_lock is aquired through the
    - * console unblank code)
    + * message out and tell the printk/console paths that an emergency
    + * message is coming through
    */
    -void bust_spinlocks(void)
    +void bust_spinlocks(int yes)
    +{
    + if (yes) {
    + oops_in_progress = 1;
    +#ifdef CONFIG_SMP
    + global_irq_lock = 0; /* Many serial drivers do __global_cli() */
    +#endif
    + } else {
    + oops_in_progress = 0;
    + /*
    + * OK, the message is on the console. Now we call printk()
    + * without oops_in_progress set so that printk will give klogd
    + * a poke. Hold onto your hats...
    + */
    + printk("");
    + }
    +}
    +
    +void do_BUG(const char *file, int line)
    {
    - spin_lock_init(&console_lock);
    - spin_lock_init(&timerlist_lock);
    + bust_spinlocks(1);
    + printk("kernel BUG at %s:%d!\n", file, line);
    }

    asmlinkage void do_invalid_op(struct pt_regs *, unsigned long);
    @@ -264,8 +284,7 @@
    * terminate things with extreme prejudice.
    */

    - bust_spinlocks();
    -
    + bust_spinlocks(1);
    if (address < PAGE_SIZE)
    printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference");
    else
    @@ -283,6 +302,7 @@
    printk(KERN_ALERT "*pte = %08lx\n", page);
    }
    die("Oops", regs, error_code);
    + bust_spinlocks(0);
    do_exit(SIGKILL);

    /*
    --- linux-2.4.0-test11-pre5/arch/i386/kernel/traps.c Wed Nov 15 23:00:16 2000
    +++ linux-akpm/arch/i386/kernel/traps.c Wed Nov 15 23:49:00 2000
    @@ -63,7 +63,7 @@
    struct desc_struct idt_table[256] __attribute__((__section__(".data.idt"))) = { {0, 0}, };

    extern int console_loglevel;
    -extern void bust_spinlocks(void);
    +extern void bust_spinlocks(int yes);

    static inline void console_silent(void)
    {
    @@ -209,9 +209,10 @@
    {
    console_verbose();
    spin_lock_irq(&die_lock);
    + bust_spinlocks(1);
    printk("%s: %04lx\n", str, err & 0xffff);
    show_registers(regs);
    -
    + bust_spinlocks(0);
    spin_unlock_irq(&die_lock);
    do_exit(SIGSEGV);
    }
    @@ -386,10 +387,14 @@
    #if CONFIG_X86_IO_APIC

    int nmi_watchdog = 1;
    +static int nmi_watchdog_verbose;

    static int __init setup_nmi_watchdog(char *str)
    {
    - get_option(&str, &nmi_watchdog);
    + if (get_option(&str, &nmi_watchdog) == 2) {
    + if (strcmp(str, "verbose") == 0)
    + nmi_watchdog_verbose = 1;
    + }
    return 1;
    }

    @@ -414,7 +419,7 @@
    * here too!]
    */

    - static unsigned int last_irq_sums [NR_CPUS],
    + static unsigned int last_irq_sums [NR_CPUS],
    alert_counter [NR_CPUS];

    /*
    @@ -437,12 +442,15 @@
    * We are in trouble anyway, lets at least try
    * to get a message out.
    */
    - bust_spinlocks();
    + bust_spinlocks(1);
    printk("NMI Watchdog detected LOCKUP on CPU%d, registers:\n", cpu);
    show_registers(regs);
    - printk("console shuts up ...\n");
    - console_silent();
    + if (nmi_watchdog_verbose == 0) {
    + printk("Console shuts up. Run dmesg or boot with `nmi_watchdog=1,verbose' for more logs\n");
    + console_silent();
    + }
    spin_unlock(&nmi_print_lock);
    + bust_spinlocks(0);
    do_exit(SIGSEGV);
    }
    } else {
    --- linux-2.4.0-test11-pre5/arch/i386/kernel/i386_ksyms.c Wed Nov 15 23:00:16 2000
    +++ linux-akpm/arch/i386/kernel/i386_ksyms.c Wed Nov 15 23:25:48 2000
    @@ -157,3 +157,5 @@
    #ifdef CONFIG_X86_PAE
    EXPORT_SYMBOL(empty_zero_page);
    #endif
    +
    +EXPORT_SYMBOL(do_BUG);
    --- linux-2.4.0-test11-pre5/drivers/char/console.c Wed Nov 15 23:00:16 2000
    +++ linux-akpm/drivers/char/console.c Wed Nov 15 23:25:48 2000
    @@ -2135,6 +2135,7 @@
    }
    }
    set_cursor(currcons);
    + poke_blanked_console();

    quit:
    clear_bit(0, &printing);
    @@ -2661,7 +2662,7 @@
    return;
    }
    console_timer.function = blank_screen;
    - if (blankinterval) {
    + if (blankinterval && !oops_in_progress) {
    mod_timer(&console_timer, jiffies + blankinterval);
    }

    @@ -2683,14 +2684,18 @@

    void poke_blanked_console(void)
    {
    - del_timer(&console_timer); /* Can't use _sync here: called from tasklet */
    - if (vt_cons[fg_console]->vc_mode == KD_GRAPHICS)
    - return;
    - if (console_blanked) {
    - console_timer.function = unblank_screen_t;
    - mod_timer(&console_timer, jiffies); /* Now */
    - } else if (blankinterval) {
    - mod_timer(&console_timer, jiffies + blankinterval);
    + if (oops_in_progress) {
    + unblank_screen(); /* Just do it */
    + } else {
    + del_timer(&console_timer); /* Can't use _sync here: called from tasklet */
    + if (vt_cons[fg_console]->vc_mode == KD_GRAPHICS)
    + return;
    + if (console_blanked) {
    + console_timer.function = unblank_screen_t;
    + mod_timer(&console_timer, jiffies); /* Now */
    + } else if (blankinterval) {
    + mod_timer(&console_timer, jiffies + blankinterval);
    + }
    }
    }

    --- linux-2.4.0-test11-pre5/Documentation/nmi_watchdog.txt Thu Aug 24 21:07:14 2000
    +++ linux-akpm/Documentation/nmi_watchdog.txt Wed Nov 15 23:25:48 2000
    @@ -24,8 +24,21 @@
    cannot even accept NMI interrupts, or the crash has made the kernel
    unable to print messages.

    -NOTE: currently the NMI-oopser is enabled unconditionally on x86 SMP
    -boxes.
    +The NMI-oopser defaults to `1' (enabled) on x86 SMP boxes.
    +
    +The NMI-oopser only displays the first oops message on the console. This
    +is to prevent vital information from scrolling off the scren if more
    +errors occur. You can find additional information (such as NMI oops
    +information from other CPUs) by looking in your system logs or with
    +the `dmesg' command.
    +
    +If your system is crashing hard and preventing you from running `dmesg'
    +you can tell the NMI oopser to display all NMI oops messages (not just
    +the first one) by setting
    +
    + nmi_watchdog=1,verbose
    +
    +on the kernel boot command line or in lilo.conf, as shown above.

    [ feel free to send bug reports, suggestions and patches to
    Ingo Molnar <mingo@redhat.com> or the Linux SMP mailing
    -
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