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From: Andrew Morton on 20 May 2010 14:40
On Thu, 20 May 2010 14:17:40 -0400
Valdis.Kletnieks(a)vt.edu wrote:

> If a process is exiting with a non-zero preempt_count, it's in fact almost
> certainly going to fail to do so because it is exiting due to a BUG or OOPS
> while it held a lock, at which point it will never actually exit. So change
> the message to say it attempted to do so, rather than implying it succeeded.
> Problem spotted when a process BUG'ed, the kernel reported the 'exited' status,
> and then proceeded to BUG twice more dealing with the now-zombied process:
>
> > [ 35.357018] note: keymap[2481] exited with preempt_count 1
> > [ 35.360503] BUG: scheduling while atomic: keymap/2481/0x10000002
>
> Yes, one line is 83 characters. It's still more readable than a split printk.
>
> Signed-off-by: Valdis Kletnieks <valdis.kletnieks(a)vt.edu>
>
> --- linux-2.6.34-mmotm0519/kernel/exit.c.dist 2010-05-20 10:59:11.646870592 -0400
> +++ linux-2.6.34-mmotm0519/kernel/exit.c 2010-05-20 14:05:16.068800223 -0400
> @@ -936,7 +936,7 @@ NORET_TYPE void do_exit(long code)
> raw_spin_unlock_wait(&tsk->pi_lock);
>
> if (unlikely(in_atomic()))
> - printk(KERN_INFO "note: %s[%d] exited with preempt_count %d\n",
> + printk(KERN_INFO "note: %s[%d] tried to exit with preempt_count %d\n",
> current->comm, task_pid_nr(current),
> preempt_count());

a) this message is kinda like __schedule_bug(), only
__schedule_bug() does more stuff. Perhaps some sharing is in order.

b) do_exit() eventually calls schedule() anyway, so if we have a bad
preempt_count() here, schedule() should end up calling
__schedule_bug(), so we don't need this message in do_exit().

ah-hah, __schedule_bug() doesn't get called on the exit() path due to
task->state==TASK_DEAD. But we can surely change that.
schedule_debug() needs fixing anyway - what's it doing assuming that
TASK_RUNNING==0?

c) it's pretty pointless printing anything at all if this task has
oopsed. This info is never interesting and will just cause the
useful info to scroll into oblivion.

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