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- Add comments about the maintenance of the per-thread list of contested

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locks held by each thread.
- Fix a bug in the original BSD/OS code where a contested lock was not
  properly handed off from the old thread to the new thread when a
  contested lock with more than one blocked thread was transferred from
  one thread to another.
- Don't use an atomic operation to write the MTX_CONTESTED value to
  mtx_lock in the aforementioned special case.  The memory barriers and
  exclusion provided by sched_lock are sufficient.

Spotted by:	alc (2)
This commit is contained in:
jhb 2003-07-02 16:14:09 +00:00
parent 17958a749f
commit 58598b39f8
2 changed files with 18 additions and 8 deletions
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13
sys/kern/kern_mutex.c
View File

@ -524,12 +524,15 @@ _mtx_lock_sleep(struct mtx *m, int opts, const char *file, int line)
/*
* The mutex was marked contested on release. This means that
* there are threads blocked on it.
* there are other threads blocked on it. Grab ownership of
* it and propagate its priority to the current thread if
* necessary.
*/
if (v == MTX_CONTESTED) {
td1 = TAILQ_FIRST(&m->mtx_blocked);
MPASS(td1 != NULL);
m->mtx_lock = (uintptr_t)td | MTX_CONTESTED;
LIST_INSERT_HEAD(&td->td_contested, m, mtx_contested);
if (td1->td_priority < td->td_priority)
td->td_priority = td1->td_priority;
@ -593,7 +596,9 @@ _mtx_lock_sleep(struct mtx *m, int opts, const char *file, int line)
#endif
/*
* Put us on the list of threads blocked on this mutex.
* Put us on the list of threads blocked on this mutex
* and add this mutex to the owning thread's list of
* contested mutexes if needed.
*/
if (TAILQ_EMPTY(&m->mtx_blocked)) {
td1 = mtx_owner(m);
@ -744,13 +749,13 @@ _mtx_unlock_sleep(struct mtx *m, int opts, const char *file, int line)
TAILQ_REMOVE(&m->mtx_blocked, td1, td_lockq);
LIST_REMOVE(m, mtx_contested);
if (TAILQ_EMPTY(&m->mtx_blocked)) {
LIST_REMOVE(m, mtx_contested);
_release_lock_quick(m);
if (LOCK_LOG_TEST(&m->mtx_object, opts))
CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p not held", m);
} else
atomic_store_rel_ptr(&m->mtx_lock, (void *)MTX_CONTESTED);
m->mtx_lock = MTX_CONTESTED;
pri = PRI_MAX;
LIST_FOREACH(m1, &td->td_contested, mtx_contested) {

13
sys/kern/subr_turnstile.c
View File

@ -524,12 +524,15 @@ _mtx_lock_sleep(struct mtx *m, int opts, const char *file, int line)
/*
* The mutex was marked contested on release. This means that
* there are threads blocked on it.
* there are other threads blocked on it. Grab ownership of
* it and propagate its priority to the current thread if
* necessary.
*/
if (v == MTX_CONTESTED) {
td1 = TAILQ_FIRST(&m->mtx_blocked);
MPASS(td1 != NULL);
m->mtx_lock = (uintptr_t)td | MTX_CONTESTED;
LIST_INSERT_HEAD(&td->td_contested, m, mtx_contested);
if (td1->td_priority < td->td_priority)
td->td_priority = td1->td_priority;
@ -593,7 +596,9 @@ _mtx_lock_sleep(struct mtx *m, int opts, const char *file, int line)
#endif
/*
* Put us on the list of threads blocked on this mutex.
* Put us on the list of threads blocked on this mutex
* and add this mutex to the owning thread's list of
* contested mutexes if needed.
*/
if (TAILQ_EMPTY(&m->mtx_blocked)) {
td1 = mtx_owner(m);
@ -744,13 +749,13 @@ _mtx_unlock_sleep(struct mtx *m, int opts, const char *file, int line)
TAILQ_REMOVE(&m->mtx_blocked, td1, td_lockq);
LIST_REMOVE(m, mtx_contested);
if (TAILQ_EMPTY(&m->mtx_blocked)) {
LIST_REMOVE(m, mtx_contested);
_release_lock_quick(m);
if (LOCK_LOG_TEST(&m->mtx_object, opts))
CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p not held", m);
} else
atomic_store_rel_ptr(&m->mtx_lock, (void *)MTX_CONTESTED);
m->mtx_lock = MTX_CONTESTED;
pri = PRI_MAX;
LIST_FOREACH(m1, &td->td_contested, mtx_contested) {