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authorAnton Blanchard <anton@samba.org>2006-03-23 02:59:20 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2006-03-23 07:38:02 -0800
commite9028b0ff2bad1954568604dc17725692c8524d6 (patch)
treedbff742d39520574e5985930333f1d421282e080
parent5be0e9511990dc307670dc66a42073db96b20f26 (diff)
[PATCH] fix scheduler deadlock
We have noticed lockups during boot when stress testing kexec on ppc64. Two cpus would deadlock in scheduler code trying to grab already taken spinlocks. The double_rq_lock code uses the address of the runqueue to order the taking of multiple locks. This address is a per cpu variable: if (rq1 < rq2) { spin_lock(&rq1->lock); spin_lock(&rq2->lock); } else { spin_lock(&rq2->lock); spin_lock(&rq1->lock); } On the other hand, the code in wake_sleeping_dependent uses the cpu id order to grab locks: for_each_cpu_mask(i, sibling_map) spin_lock(&cpu_rq(i)->lock); This means we rely on the address of per cpu data increasing as cpu ids increase. While this will be true for the generic percpu implementation it may not be true for arch specific implementations. One way to solve this is to always take runqueues in cpu id order. To do this we add a cpu variable to the runqueue and check it in the double runqueue locking functions. Signed-off-by: Anton Blanchard <anton@samba.org> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--kernel/sched.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 6b6e0d70eb3..a5bd60453ea 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -237,6 +237,7 @@ struct runqueue {
task_t *migration_thread;
struct list_head migration_queue;
+ int cpu;
#endif
#ifdef CONFIG_SCHEDSTATS
@@ -1654,6 +1655,9 @@ unsigned long nr_iowait(void)
/*
* double_rq_lock - safely lock two runqueues
*
+ * We must take them in cpu order to match code in
+ * dependent_sleeper and wake_dependent_sleeper.
+ *
* Note this does not disable interrupts like task_rq_lock,
* you need to do so manually before calling.
*/
@@ -1665,7 +1669,7 @@ static void double_rq_lock(runqueue_t *rq1, runqueue_t *rq2)
spin_lock(&rq1->lock);
__acquire(rq2->lock); /* Fake it out ;) */
} else {
- if (rq1 < rq2) {
+ if (rq1->cpu < rq2->cpu) {
spin_lock(&rq1->lock);
spin_lock(&rq2->lock);
} else {
@@ -1701,7 +1705,7 @@ static void double_lock_balance(runqueue_t *this_rq, runqueue_t *busiest)
__acquires(this_rq->lock)
{
if (unlikely(!spin_trylock(&busiest->lock))) {
- if (busiest < this_rq) {
+ if (busiest->cpu < this_rq->cpu) {
spin_unlock(&this_rq->lock);
spin_lock(&busiest->lock);
spin_lock(&this_rq->lock);
@@ -6029,6 +6033,7 @@ void __init sched_init(void)
rq->push_cpu = 0;
rq->migration_thread = NULL;
INIT_LIST_HEAD(&rq->migration_queue);
+ rq->cpu = i;
#endif
atomic_set(&rq->nr_iowait, 0);