[BK PATCH 2.5.6-pre2] fix task migration code boot hang

[BK PATCH 2.5.6-pre2] fix task migration code boot hang

[James Bottomley]

[-- Attachment #1: Type: text/plain, Size: 269 bytes --]

The task migration code of change set 1.373 actually only works on 
architectures where the physical and logical CPU numberings are the same. It 
they aren't, the boot sequence hangs forever. The attached fixes the code to 
work on all architectures.

James Bottomley


[-- Attachment #2: migrate.diff --]
[-- Type: text/plain , Size: 2802 bytes --]

# This is a BitKeeper generated patch for the following project:
# Project Name: Linux kernel tree
# This patch format is intended for GNU patch command version 2.5 or higher.
# This patch includes the following deltas:
#	           ChangeSet	1.425   -> 1.426  
#	      kernel/sched.c	1.51    -> 1.52   
#
# The following is the BitKeeper ChangeSet Log
# --------------------------------------------
# 02/02/27	jejb@malley.hansenpartnership.com	1.426
# Fix new SMP migration thread code (introduced in change set 1.373)
# 
# - make migration_mask a logical bitmap with correct conversions.
# --------------------------------------------
#
diff -Nru a/kernel/sched.c b/kernel/sched.c
--- a/kernel/sched.c	Wed Feb 27 15:04:46 2002
+++ b/kernel/sched.c	Wed Feb 27 15:04:46 2002
@@ -1555,7 +1555,8 @@
 	down(&req.sem);
 }
 
-static volatile unsigned long migration_mask;
+/* NOTE: migration_mask is a bitmap of logical CPUs */
+static volatile unsigned long migration_mask = 0;
 
 static int migration_thread(void * unused)
 {
@@ -1585,7 +1586,8 @@
 
 	for (;;) {
 		preempt_disable();
-		if (test_and_clear_bit(smp_processor_id(), &migration_mask))
+		if (test_and_clear_bit(cpu_number_map(smp_processor_id()),
+				       &migration_mask))
 			current->cpus_allowed = 1 << smp_processor_id();
 		if (test_thread_flag(TIF_NEED_RESCHED))
 			schedule();
@@ -1656,7 +1658,7 @@
 	migration_mask = (1 << smp_num_cpus) - 1;
 
 	for (cpu = 0; cpu < smp_num_cpus; cpu++)
-		while (!cpu_rq(cpu)->migration_thread)
+		while (!cpu_rq(cpu_logical_map(cpu))->migration_thread)
 			schedule_timeout(2);
 	if (migration_mask)
 		BUG();
This BitKeeper patch contains the following changesets:
+
## Wrapped with gzip_uu ##


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end

Re: [BK PATCH 2.5.6-pre2] fix task migration code boot hang

[Ingo Molnar]

On Wed, 27 Feb 2002, James Bottomley wrote:

> The task migration code of change set 1.373 actually only works on
> architectures where the physical and logical CPU numberings are the
> same. It they aren't, the boot sequence hangs forever. The attached
> fixes the code to work on all architectures.

yep. DaveM has sent me a fix for this already which is in my tree.

	Ingo