I ran into the bug on 2.6.17-rt8 with the previous posted patches which
make pthread_timed_lock() work on UP, but the bug is there without the
patches - I just can't trigger it - and it is also in the mainline kernel.
The problem is that rt_mutex_next_owner() is used unprotected in
wake_futex_pi(). At least it isn't probably serialiazed against the next
owner being signalled or getting a timeout. The only lock, which is
good enough here, is &pi_state->pi_mutex.wait_lock, so I added this
protection.
Esben
kernel/futex.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
Index: linux-2.6.17-rt8/kernel/futex.c
===================================================================
--- linux-2.6.17-rt8.orig/kernel/futex.c
+++ linux-2.6.17-rt8/kernel/futex.c
@@ -565,6 +565,7 @@ static int wake_futex_pi(u32 __user *uad
if (!pi_state)
return -EINVAL;
+ spin_lock(&pi_state->pi_mutex.wait_lock);
new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
/*
@@ -590,15 +591,22 @@ static int wake_futex_pi(u32 __user *uad
curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
dec_preempt_count();
- if (curval == -EFAULT)
+ if (curval == -EFAULT) {
+ spin_unlock(&pi_state->pi_mutex.wait_lock);
return -EFAULT;
- if (curval != uval)
+ }
+ if (curval != uval) {
+ spin_unlock(&pi_state->pi_mutex.wait_lock);
return -EINVAL;
+ }
list_del_init(&pi_state->owner->pi_state_list);
list_add(&pi_state->list, &new_owner->pi_state_list);
pi_state->owner = new_owner;
+ atomic_inc(&pi_state->refcount);
+ spin_unlock(&pi_state->pi_mutex.wait_lock);
rt_mutex_unlock(&pi_state->pi_mutex);
+ free_pi_state(pi_state);
return 0;
}
-
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