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  1. Jul 25, 2008
  3. Jul 24, 2008
  5. Jul 23, 2008
    • Jason Wessel's avatar
      kgdb, powerpc: arch specific powerpc kgdb support · 17ce452f
      Jason Wessel authored 
      

This patch removes the old kgdb reminants from ARCH=powerpc and
implements the new style arch specific stub for the common kgdb core
interface.

It is possible to have xmon and kgdb in the same kernel, but you
cannot use both at the same time because there is only one set of
debug hooks.

The arch specific kgdb implementation saves the previous state of the
debug hooks and restores them if you unconfigure the kgdb I/O driver.
Kgdb should have no impact on a kernel that has no kgdb I/O driver
configured.

Signed-off-by: default avatarJason Wessel <jason.wessel@windriver.com>
      17ce452f
  7. Jul 22, 2008
  9. Jul 18, 2008
    • Thomas Gleixner's avatar
      nohz: prevent tick stop outside of the idle loop · b8f8c3cf
      Thomas Gleixner authored 
      

Jack Ren and Eric Miao tracked down the following long standing
problem in the NOHZ code:

	scheduler switch to idle task
	enable interrupts

Window starts here

	----> interrupt happens (does not set NEED_RESCHED)
	      	irq_exit() stops the tick

	----> interrupt happens (does set NEED_RESCHED)

	return from schedule()
	
	cpu_idle(): preempt_disable();

Window ends here

The interrupts can happen at any point inside the race window. The
first interrupt stops the tick, the second one causes the scheduler to
rerun and switch away from idle again and we end up with the tick
disabled.

The fact that it needs two interrupts where the first one does not set
NEED_RESCHED and the second one does made the bug obscure and extremly
hard to reproduce and analyse. Kudos to Jack and Eric.

Solution: Limit the NOHZ functionality to the idle loop to make sure
that we can not run into such a situation ever again.

cpu_idle()
{
	preempt_disable();

	while(1) {
		 tick_nohz_stop_sched_tick(1); <- tell NOHZ code that we
		 			          are in the idle loop

		 while (!need_resched())
		       halt();

		 tick_nohz_restart_sched_tick(); <- disables NOHZ mode
		 preempt_enable_no_resched();
		 schedule();
		 preempt_disable();
	}
}

In hindsight we should have done this forever, but ... 

/me grabs a large brown paperbag.

Debugged-by: default avatarJack Ren <jack.ren@marvell.com&gt;,>
Debugged-by: default avatareric miao <eric.y.miao@gmail.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      b8f8c3cf
  11. Jul 16, 2008
  13. Jul 15, 2008
  15. Jul 14, 2008