- Fix a race in sched_switch() of sched_4bsd.

  In the case of the thread being on a sleepqueue or a turnstile, the
  sched_lock was acquired (without the aid of the td_lock interface) and
  the td_lock was dropped. This was going to break locking rules on other
  threads willing to access to the thread (via the td_lock interface) and
  modify his flags (allowed as long as the container lock was different
  by the one used in sched_switch).
  In order to prevent this situation, while sched_lock is acquired there
  the td_lock gets blocked. [0]
- Merge the ULE's internal function thread_block_switch() into the global
  thread_lock_block() and make the former semantic as the default for
  thread_lock_block(). This means that thread_lock_block() will not
  disable interrupts when called (and consequently thread_unlock_block()
  will not re-enabled them when called). This should be done manually
  when necessary.
  Note, however, that ULE's thread_unblock_switch() is not reaped
  because it does reflect a difference in semantic due in ULE (the
  td_lock may not be necessarilly still blocked_lock when calling this).
  While asymmetric, it does describe a remarkable difference in semantic
  that is good to keep in mind.

[0] Reported by:	Kohji Okuno
			<okuno dot kohji at jp dot panasonic dot com>
Tested by:		Giovanni Trematerra
			<giovanni dot trematerra at gmail dot com>
MFC:			2 weeks

1 files changed, 0 insertions, 2 deletions

diff --git a/sys/kern/kern_mutex.c b/sys/kern/kern_mutex.c
index 85ca646..f9c3377 100644
--- a/sys/kern/kern_mutex.c
+++ b/sys/kern/kern_mutex.c
@@ -616,7 +616,6 @@ thread_lock_block(struct thread *td)
 {
 	struct mtx *lock;
 
-	spinlock_enter();
 	THREAD_LOCK_ASSERT(td, MA_OWNED);
 	lock = td->td_lock;
 	td->td_lock = &blocked_lock;
@@ -631,7 +630,6 @@ thread_lock_unblock(struct thread *td, struct mtx *new)
 	mtx_assert(new, MA_OWNED);
 	MPASS(td->td_lock == &blocked_lock);
 	atomic_store_rel_ptr((volatile void *)&td->td_lock, (uintptr_t)new);
-	spinlock_exit();
 }
 
 void