[PATCH] scheduler: migration_task deadlock

[Erich Focht]

Hi,

in the migration scheme included into the 2.5.6-pre1 kernel there is a
potential deadlock (which I encountered several times) in the migration
task. If interrupts are not disabled before aquiring the double rq lock
this task can be interrupted by a scheduler_tick() which will spinwait
forever.

Best regards,
Erich

diff -urN 2.5.6-pre1/kernel/sched.c 2.5.6-pre1-fix/kernel/sched.c
--- 2.5.6-pre1/kernel/sched.c	Thu Feb 28 19:10:49 2002
+++ 2.5.6-pre1-fix/kernel/sched.c	Thu Feb 28 19:14:29 2002
@@ -1626,9 +1626,11 @@
 		cpu_src = p->thread_info->cpu;
 		rq_src = cpu_rq(cpu_src);
 
+		local_irq_save(flags);
 		double_rq_lock(rq_src, rq_dest);
 		if (p->thread_info->cpu != cpu_src) {
 			double_rq_unlock(rq_src, rq_dest);
+			local_irq_restore(flags);
 			goto repeat;
 		}
 		if (rq_src == rq) {
@@ -1639,6 +1641,7 @@
 			}
 		}
 		double_rq_unlock(rq_src, rq_dest);
+		local_irq_restore(flags);
 
 		up(&req->sem);
 	}