Russ Anderson wrote:
Keith Owens wrote:The existing 'oops_in_progress' code is working pretty well. It does leave nasty bits behind if the MCA is recoverable, but that problem is not bad enough to justify a completely separate print mechanism plus changes to external programs. Instead we should fix the unwanted side effects of oops_in_progress.One problem is that oops_in_progress gets set in MCA/INIT but does not get cleared if the MCA is recovered (or after the INIT stack trace prints). The result is that subsequent messages donot get to /var/log/messages, due to release_console_sem() not waking up klogd. Thanks to Keith Owens for his analysis of this problem.This patch does not address the larger issue of printing from MCA/INIT context.
Still there are larger issues...
Here are related codes in kernel/printk.c(2.6.17):
418 static void zap_locks(void)
419 {
420 static unsigned long oops_timestamp;
421
422 if (time_after_eq(jiffies, oops_timestamp) &&
423 !time_after(jiffies, oops_timestamp + 30 * HZ))
424 return;
425
426 oops_timestamp = jiffies;
427
428 /* If a crash is occurring, make sure we can't deadlock */
429 spin_lock_init(&logbuf_lock);
430 /* And make sure that we print immediately */
431 init_MUTEX(&console_sem);
432 }
490 asmlinkage int vprintk(const char *fmt, va_list args)
491 {
492 unsigned long flags;
493 int printed_len;
494 char *p;
495 static char printk_buf[1024];
496 static int log_level_unknown = 1;
497
498 preempt_disable();
499 if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
500 /* If a crash is occurring during printk() on this CPU,
501 * make sure we can't deadlock */
502 zap_locks();
503
504 /* This stops the holder of console_sem just where we want him */
505 spin_lock_irqsave(&logbuf_lock, flags);
506 printk_cpu = smp_processor_id();
It seems that there are at least two problems not solved yet.
- zap_lock initializes console_sem. It doesn't wake up waiters.
- it allows existence of two holders of logbuf_lock if interrupted
original holder restarts after spin_lock_init(logbuf_lock).
You'll see mixed message like: inrterecruovepteredd
These larger issues are more critical and need to be solved before
returning from MCA/INIT handlers saying "recovered".
And these issues are no matter if the kernel is really progressing oops.
H.Seto
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