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Message-ID: <alpine.LFD.2.02.1304151414341.21884@ionos>
Date: Mon, 15 Apr 2013 14:16:10 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: Linus Torvalds <torvalds@...ux-foundation.org>
cc: Andrew Morton <akpm@...ux-foundation.org>,
Ingo Molnar <mingo@...nel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: [GIT pull] core fixes for 3.9
Linus,
please pull the latest core-urgent-for-linus git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git core-urgent-for-linus
* A single bugfix which plugs two race confitions which can cause
hotplug per cpu threads to end up on the wrong cpu.
Thanks,
tglx
------------------>
Thomas Gleixner (1):
kthread: Prevent unpark race which puts threads on the wrong cpu
fs/proc/array.c | 1 +
include/linux/sched.h | 5 ++-
include/trace/events/sched.h | 2 +-
kernel/kthread.c | 52 ++++++++++++++++++++++-------------------
kernel/smpboot.c | 14 +++++++++-
5 files changed, 45 insertions(+), 29 deletions(-)
diff --git a/fs/proc/array.c b/fs/proc/array.c
index f7ed9ee..cbd0f1b 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -143,6 +143,7 @@ static const char * const task_state_array[] = {
"x (dead)", /* 64 */
"K (wakekill)", /* 128 */
"W (waking)", /* 256 */
+ "P (parked)", /* 512 */
};
static inline const char *get_task_state(struct task_struct *tsk)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index d35d2b6..e692a02 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -163,9 +163,10 @@ print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
#define TASK_DEAD 64
#define TASK_WAKEKILL 128
#define TASK_WAKING 256
-#define TASK_STATE_MAX 512
+#define TASK_PARKED 512
+#define TASK_STATE_MAX 1024
-#define TASK_STATE_TO_CHAR_STR "RSDTtZXxKW"
+#define TASK_STATE_TO_CHAR_STR "RSDTtZXxKWP"
extern char ___assert_task_state[1 - 2*!!(
sizeof(TASK_STATE_TO_CHAR_STR)-1 != ilog2(TASK_STATE_MAX)+1)];
diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 5a8671e..e5586ca 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -147,7 +147,7 @@ TRACE_EVENT(sched_switch,
__print_flags(__entry->prev_state & (TASK_STATE_MAX-1), "|",
{ 1, "S"} , { 2, "D" }, { 4, "T" }, { 8, "t" },
{ 16, "Z" }, { 32, "X" }, { 64, "x" },
- { 128, "W" }) : "R",
+ { 128, "K" }, { 256, "W" }, { 512, "P" }) : "R",
__entry->prev_state & TASK_STATE_MAX ? "+" : "",
__entry->next_comm, __entry->next_pid, __entry->next_prio)
);
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 691dc2e..9eb7fed 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -124,12 +124,12 @@ void *kthread_data(struct task_struct *task)
static void __kthread_parkme(struct kthread *self)
{
- __set_current_state(TASK_INTERRUPTIBLE);
+ __set_current_state(TASK_PARKED);
while (test_bit(KTHREAD_SHOULD_PARK, &self->flags)) {
if (!test_and_set_bit(KTHREAD_IS_PARKED, &self->flags))
complete(&self->parked);
schedule();
- __set_current_state(TASK_INTERRUPTIBLE);
+ __set_current_state(TASK_PARKED);
}
clear_bit(KTHREAD_IS_PARKED, &self->flags);
__set_current_state(TASK_RUNNING);
@@ -256,8 +256,13 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
}
EXPORT_SYMBOL(kthread_create_on_node);
-static void __kthread_bind(struct task_struct *p, unsigned int cpu)
+static void __kthread_bind(struct task_struct *p, unsigned int cpu, long state)
{
+ /* Must have done schedule() in kthread() before we set_task_cpu */
+ if (!wait_task_inactive(p, state)) {
+ WARN_ON(1);
+ return;
+ }
/* It's safe because the task is inactive. */
do_set_cpus_allowed(p, cpumask_of(cpu));
p->flags |= PF_THREAD_BOUND;
@@ -274,12 +279,7 @@ static void __kthread_bind(struct task_struct *p, unsigned int cpu)
*/
void kthread_bind(struct task_struct *p, unsigned int cpu)
{
- /* Must have done schedule() in kthread() before we set_task_cpu */
- if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE)) {
- WARN_ON(1);
- return;
- }
- __kthread_bind(p, cpu);
+ __kthread_bind(p, cpu, TASK_UNINTERRUPTIBLE);
}
EXPORT_SYMBOL(kthread_bind);
@@ -324,6 +324,22 @@ static struct kthread *task_get_live_kthread(struct task_struct *k)
return NULL;
}
+static void __kthread_unpark(struct task_struct *k, struct kthread *kthread)
+{
+ clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
+ /*
+ * We clear the IS_PARKED bit here as we don't wait
+ * until the task has left the park code. So if we'd
+ * park before that happens we'd see the IS_PARKED bit
+ * which might be about to be cleared.
+ */
+ if (test_and_clear_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
+ if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
+ __kthread_bind(k, kthread->cpu, TASK_PARKED);
+ wake_up_state(k, TASK_PARKED);
+ }
+}
+
/**
* kthread_unpark - unpark a thread created by kthread_create().
* @k: thread created by kthread_create().
@@ -336,20 +352,8 @@ void kthread_unpark(struct task_struct *k)
{
struct kthread *kthread = task_get_live_kthread(k);
- if (kthread) {
- clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
- /*
- * We clear the IS_PARKED bit here as we don't wait
- * until the task has left the park code. So if we'd
- * park before that happens we'd see the IS_PARKED bit
- * which might be about to be cleared.
- */
- if (test_and_clear_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
- if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
- __kthread_bind(k, kthread->cpu);
- wake_up_process(k);
- }
- }
+ if (kthread)
+ __kthread_unpark(k, kthread);
put_task_struct(k);
}
@@ -407,7 +411,7 @@ int kthread_stop(struct task_struct *k)
trace_sched_kthread_stop(k);
if (kthread) {
set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
- clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
+ __kthread_unpark(k, kthread);
wake_up_process(k);
wait_for_completion(&kthread->exited);
}
diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index 8eaed9a..02fc5c9 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -185,8 +185,18 @@ __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
}
get_task_struct(tsk);
*per_cpu_ptr(ht->store, cpu) = tsk;
- if (ht->create)
- ht->create(cpu);
+ if (ht->create) {
+ /*
+ * Make sure that the task has actually scheduled out
+ * into park position, before calling the create
+ * callback. At least the migration thread callback
+ * requires that the task is off the runqueue.
+ */
+ if (!wait_task_inactive(tsk, TASK_PARKED))
+ WARN_ON(1);
+ else
+ ht->create(cpu);
+ }
return 0;
}
--
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