From: Rusty Russell <rusty@rustcorp.com.au>
Someone is triggering the WARN_ON() in futex.c. We know that software
suspend could do it, in theory. But noone else should be.
This code adds a PF_FUTEX_DEBUG flag, which is set in the futex code
when we sleep, and also when we wake up. If a task with
PF_FUTEX_DEBUG is woken by a task without PF_FUTEX_DEBUG, we have
found our culprit.
---
include/linux/sched.h | 1 +
kernel/futex.c | 15 +++++++++++++--
kernel/sched.c | 8 ++++++++
kernel/timer.c | 12 +++++++++++-
4 files changed, 33 insertions(+), 3 deletions(-)
diff -puN include/linux/sched.h~futex_wait-debug include/linux/sched.h
--- 25/include/linux/sched.h~futex_wait-debug 2004-03-08 23:27:30.000000000 -0800
+++ 25-akpm/include/linux/sched.h 2004-03-08 23:27:30.000000000 -0800
@@ -532,6 +532,7 @@ do { if (atomic_dec_and_test(&(tsk)->usa
#define PF_SWAPOFF 0x00080000 /* I am in swapoff */
#define PF_LESS_THROTTLE 0x00100000 /* Throttle me less: I clean memory */
#define PF_SYNCWRITE 0x00200000 /* I am doing a sync write */
+#define PF_FUTEX_DEBUG 0x00400000
#ifdef CONFIG_SMP
#define SCHED_LOAD_SHIFT 7 /* increase resolution of load calculations */
diff -puN kernel/futex.c~futex_wait-debug kernel/futex.c
--- 25/kernel/futex.c~futex_wait-debug 2004-03-08 23:27:30.000000000 -0800
+++ 25-akpm/kernel/futex.c 2004-03-08 23:27:30.000000000 -0800
@@ -269,7 +269,11 @@ static void wake_futex(struct futex_q *q
* The lock in wake_up_all() is a crucial memory barrier after the
* list_del_init() and also before assigning to q->lock_ptr.
*/
+
+ current->flags |= PF_FUTEX_DEBUG;
wake_up_all(&q->waiters);
+ current->flags &= ~PF_FUTEX_DEBUG;
+
/*
* The waiting task can free the futex_q as soon as this is written,
* without taking any locks. This must come last.
@@ -490,8 +494,11 @@ static int futex_wait(unsigned long uadd
* !list_empty() is safe here without any lock.
* q.lock_ptr != 0 is not safe, because of ordering against wakeup.
*/
- if (likely(!list_empty(&q.list)))
+ if (likely(!list_empty(&q.list))) {
+ current->flags |= PF_FUTEX_DEBUG;
time = schedule_timeout(time);
+ current->flags &= ~PF_FUTEX_DEBUG;
+ }
__set_current_state(TASK_RUNNING);
/*
@@ -505,7 +512,11 @@ static int futex_wait(unsigned long uadd
if (time == 0)
return -ETIMEDOUT;
/* A spurious wakeup should never happen. */
- WARN_ON(!signal_pending(current));
+ if (!signal_pending(current)) {
+ printk("futex_wait woken: %lu %i %lu\n",
+ uaddr, val, time);
+ WARN_ON(1);
+ }
return -EINTR;
out_unqueue:
diff -puN kernel/sched.c~futex_wait-debug kernel/sched.c
--- 25/kernel/sched.c~futex_wait-debug 2004-03-08 23:27:30.000000000 -0800
+++ 25-akpm/kernel/sched.c 2004-03-08 23:27:30.000000000 -0800
@@ -761,6 +761,14 @@ static int try_to_wake_up(task_t * p, un
}
goto out_activate;
+ if ((p->flags & PF_FUTEX_DEBUG)
+ && !(current->flags & PF_FUTEX_DEBUG)) {
+ printk("%s %i waking %s: %i %i\n",
+ current->comm, (int)in_interrupt(),
+ p->comm, p->tgid, p->pid);
+ WARN_ON(1);
+ }
+
repeat_lock_task:
task_rq_unlock(rq, &flags);
rq = task_rq_lock(p, &flags);
diff -puN kernel/timer.c~futex_wait-debug kernel/timer.c
--- 25/kernel/timer.c~futex_wait-debug 2004-03-08 23:27:30.000000000 -0800
+++ 25-akpm/kernel/timer.c 2004-03-08 23:27:30.000000000 -0800
@@ -971,6 +971,13 @@ static void process_timeout(unsigned lon
wake_up_process((task_t *)__data);
}
+static void futex_timeout(unsigned long __data)
+{
+ current->flags |= PF_FUTEX_DEBUG;
+ wake_up_process((task_t *)__data);
+ current->flags &= ~PF_FUTEX_DEBUG;
+}
+
/**
* schedule_timeout - sleep until timeout
* @timeout: timeout value in jiffies
@@ -1037,7 +1044,10 @@ fastcall signed long schedule_timeout(si
init_timer(&timer);
timer.expires = expire;
timer.data = (unsigned long) current;
- timer.function = process_timeout;
+ if (current->flags & PF_FUTEX_DEBUG)
+ timer.function = futex_timeout;
+ else
+ timer.function = process_timeout;
add_timer(&timer);
schedule();
_