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

commit e668fa1aea7844ac4c7ea09030a2f3e647a4adb1
Author: Andi Kleen <ak@linux.intel.com>
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@linux.intel.com>

---
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);
+}
+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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