Re: [patch] sched: unlocked context-switches

[David S. Miller]

On Sat, 9 Apr 2005 00:15:37 -0700
David Mosberger <davidm@xxxxxxxxxxxxxxxxx> wrote:

> Yes, of course.  The deadlock was due to context-switching, not
> switch_mm() per se.  Hopefully someone else beats me to remembering
> the details before Monday.

Sparc64 has a deadlock because we hold mm->page_table_lock during
switch_mm().  I bet IA64 did something similar, as I remember it
had a very similar locking issue in this area.

So the deadlock was, we held the runqueue locks over switch_mm(),
switch_mm() spins on mm->page_table_lock, the cpu which does have
mm->page_table_lock tries to do a wakeup on the first cpu's runqueue.
Classic AB-BA deadlock.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/