Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=ce96b5ac742801718ae86d2adf0500c5abef3782
Commit: ce96b5ac742801718ae86d2adf0500c5abef3782
Parent: dae51f56204d33444f61d9e7af3ee70aef55daa4
Author: Dmitry Adamushko <[EMAIL PROTECTED]>
AuthorDate: Thu Nov 15 20:57:40 2007 +0100
Committer: Ingo Molnar <[EMAIL PROTECTED]>
CommitDate: Thu Nov 15 20:57:40 2007 +0100
sched: fix __set_task_cpu() SMP race
Grant Wilson has reported rare SCHED_FAIR_USER crashes on his quad-core
system, which crashes can only be explained via runqueue corruption.
there is a narrow SMP race in __set_task_cpu(): after ->cpu is set up to
a new value, task_rq_lock(p, ...) can be successfuly executed on another
CPU. We must ensure that updates of per-task data have been completed by
this moment.
this bug has been hiding in the Linux scheduler for an eternity (we never
had any explicit barrier for task->cpu in set_task_cpu() - so the bug was
introduced in 2.5.1), but only became visible via set_task_cfs_rq() being
accidentally put after the task->cpu update. It also probably needs a
sufficiently out-of-order CPU to trigger.
Reported-by: Grant Wilson <[EMAIL PROTECTED]>
Signed-off-by: Dmitry Adamushko <[EMAIL PROTECTED]>
Signed-off-by: Ingo Molnar <[EMAIL PROTECTED]>
---
kernel/sched.c | 20 +++++++++++++-------
1 files changed, 13 insertions(+), 7 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index d62b759..db1f71e 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -216,15 +216,15 @@ static inline struct task_group *task_group(struct
task_struct *p)
}
/* Change a task's cfs_rq and parent entity if it moves across CPUs/groups */
-static inline void set_task_cfs_rq(struct task_struct *p)
+static inline void set_task_cfs_rq(struct task_struct *p, unsigned int cpu)
{
- p->se.cfs_rq = task_group(p)->cfs_rq[task_cpu(p)];
- p->se.parent = task_group(p)->se[task_cpu(p)];
+ p->se.cfs_rq = task_group(p)->cfs_rq[cpu];
+ p->se.parent = task_group(p)->se[cpu];
}
#else
-static inline void set_task_cfs_rq(struct task_struct *p) { }
+static inline void set_task_cfs_rq(struct task_struct *p, unsigned int cpu) { }
#endif /* CONFIG_FAIR_GROUP_SCHED */
@@ -1022,10 +1022,16 @@ unsigned long weighted_cpuload(const int cpu)
static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu)
{
+ set_task_cfs_rq(p, cpu);
#ifdef CONFIG_SMP
+ /*
+ * After ->cpu is set up to a new value, task_rq_lock(p, ...) can be
+ * successfuly executed on another CPU. We must ensure that updates of
+ * per-task data have been completed by this moment.
+ */
+ smp_wmb();
task_thread_info(p)->cpu = cpu;
#endif
- set_task_cfs_rq(p);
}
#ifdef CONFIG_SMP
@@ -7088,7 +7094,7 @@ void sched_move_task(struct task_struct *tsk)
rq = task_rq_lock(tsk, &flags);
if (tsk->sched_class != &fair_sched_class) {
- set_task_cfs_rq(tsk);
+ set_task_cfs_rq(tsk, task_cpu(tsk));
goto done;
}
@@ -7103,7 +7109,7 @@ void sched_move_task(struct task_struct *tsk)
tsk->sched_class->put_prev_task(rq, tsk);
}
- set_task_cfs_rq(tsk);
+ set_task_cfs_rq(tsk, task_cpu(tsk));
if (on_rq) {
if (unlikely(running))
-
To unsubscribe from this list: send the line "unsubscribe git-commits-head" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
