Re: [Patch 1/6] XPANIC: Add extended panic interface

[richard -rw- weinberger]

On Thu, May 26, 2011 at 7:12 PM, K.Prasad <prasad@xxxxxxxxxxxxxxxxxx> wrote:
>
> commit e668fa1aea7844ac4c7ea09030a2f3e647a4adb1
> Author: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Date:   Fri Nov 19 18:36:44 2010 +0100
>
>    XPANIC: Add extended panic interface
>
>    One panic size doesn't fit all.
>
>    Machine check has some special requirements on panic, like:
>    - It wants to do a reboot timeout by default so that the machine
>    check event can be logged to disk after warm reboot.
>    - For memory errors it usually doesn't want to do crash dumps because
>    that can lead to crash loops (dumping corrupted memory would
>    lead to another machine check)
>    - It doesn't want to do backtraces because machine checks
>    are not a kernel bug.
>
>    In a earlier patch this was done with various adhoc hacks,
>    but it's cleaner to extend panic to a 'xpanic' that directly
>    gets a flag and timeout argument.
>
>    The only user right now will be x86 machine checks, but I consider
>    it likely that other users will switch to this too.
>
>    For example one obvious candidate would be the "no root
>    found" panic which doesn't really deserve a backtrace.
>
>    I exported a vpanic() interface too as a global. That's not
>    needed by the current user, but the interface has to exist
>    internally anyways and I could see how other code would
>    find a v* variant of panic useful.
>
>    Originally based on a suggestion by H. Peter Anvin.
>    Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
>
> ---
>  include/linux/kernel.h |   11 +++++++++++
>  kernel/panic.c         |   41 +++++++++++++++++++++++++++++++----------
>  2 files changed, 42 insertions(+), 10 deletions(-)
>
> Index: linux-2.6.slim_kdump/include/linux/kernel.h
> ===================================================================
> --- linux-2.6.slim_kdump.orig/include/linux/kernel.h
> +++ linux-2.6.slim_kdump/include/linux/kernel.h
> @@ -175,10 +175,21 @@ static inline void might_fault(void)
>  }
>  #endif
>
> +enum panic_flags {
> +       PANIC_NO_KEXEC     = (1 << 0),
> +       PANIC_NO_BACKTRACE = (1 << 1),
> +};
> +
>  extern struct atomic_notifier_head panic_notifier_list;
>  extern long (*panic_blink)(int state);
>  NORET_TYPE void panic(const char * fmt, ...)
>        __attribute__ ((NORET_AND format (printf, 1, 2))) __cold;
> +NORET_TYPE void xpanic(enum panic_flags flags, int timeout,
> +                      const char *fmt, ...)
> +       __attribute__ ((NORET_AND format (printf, 3, 4))) __cold;
> +NORET_TYPE void vpanic(enum panic_flags flags, int timeout,
> +                      const char *fmt,
> +                      va_list ap) __noreturn __cold;
>  extern void oops_enter(void);
>  extern void oops_exit(void);
>  void print_oops_end_marker(void);
> Index: linux-2.6.slim_kdump/kernel/panic.c
> ===================================================================
> --- linux-2.6.slim_kdump.orig/kernel/panic.c
> +++ linux-2.6.slim_kdump/kernel/panic.c
> @@ -57,14 +57,37 @@ EXPORT_SYMBOL(panic_blink);
>  *
>  *     This function never returns.
>  */
> -NORET_TYPE void panic(const char * fmt, ...)
> +NORET_TYPE void panic(const char *fmt, ...)
> +{
> +       va_list ap;
> +       va_start(ap, fmt);
> +       vpanic(0, 0, fmt, ap);
> +}
> +EXPORT_SYMBOL(panic);
> +
> +NORET_TYPE void xpanic(enum panic_flags flags, int timeout,
> +                       const char *fmt, ...)
> +{
> +       va_list ap;
> +       va_start(ap, fmt);
> +       xpanic(flags, timeout, fmt, ap);

Why are you calling xpanic() here again?
I guess you meant vpanic().

> +}
> +EXPORT_SYMBOL(xpanic);
> +
> +NORET_TYPE void vpanic(enum panic_flags flags, int timeout,
> +                      const char * fmt, va_list args)
>  {
>        static char buf[1024];
> -       va_list args;
>        long i, i_next = 0;
>        int state = 0;
>
>        /*
> +        * Let user always override panic_timeout.
> +        */
> +       if (panic_timeout > 0)
> +               timeout = panic_timeout;
> +
> +       /*
>         * It's possible to come here directly from a panic-assertion and
>         * not have preempt disabled. Some functions called from here want
>         * preempt to be disabled. No point enabling it later though...
> @@ -73,12 +96,11 @@ NORET_TYPE void panic(const char * fmt,
>
>        console_verbose();
>        bust_spinlocks(1);
> -       va_start(args, fmt);
>        vsnprintf(buf, sizeof(buf), fmt, args);
> -       va_end(args);
>        printk(KERN_EMERG "Kernel panic - not syncing: %s\n",buf);
>  #ifdef CONFIG_DEBUG_BUGVERBOSE
> -       dump_stack();
> +       if (!(flags & PANIC_NO_BACKTRACE))
> +               dump_stack();
>  #endif
>
>        /*
> @@ -86,7 +108,8 @@ NORET_TYPE void panic(const char * fmt,
>         * everything else.
>         * Do we want to call this before we try to display a message?
>         */
> -       crash_kexec(NULL);
> +       if (!(flags & PANIC_NO_KEXEC))
> +               crash_kexec(NULL);
>
>        kmsg_dump(KMSG_DUMP_PANIC);
>
> @@ -104,7 +127,7 @@ NORET_TYPE void panic(const char * fmt,
>        if (!panic_blink)
>                panic_blink = no_blink;
>
> -       if (panic_timeout > 0) {
> +       if (timeout > 0) {
>                /*
>                 * Delay timeout seconds before rebooting the machine.
>                 * We can't use the "normal" timers since we just panicked.
> @@ -152,9 +175,7 @@ NORET_TYPE void panic(const char * fmt,
>                mdelay(PANIC_TIMER_STEP);
>        }
>  }
> -
> -EXPORT_SYMBOL(panic);
> -
> +EXPORT_SYMBOL(vpanic);
>
>  struct tnt {
>        u8      bit;
> --
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-- 
Thanks,
//richard
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