diff --git a/include/sys/dsl_pool.h b/include/sys/dsl_pool.h index b2b9128e52..48b12e8eb1 100644 --- a/include/sys/dsl_pool.h +++ b/include/sys/dsl_pool.h @@ -156,6 +156,7 @@ void dsl_pool_mos_diduse_space(dsl_pool_t *dp, int64_t used, int64_t comp, int64_t uncomp); boolean_t dsl_pool_need_dirty_delay(dsl_pool_t *dp); void dsl_pool_config_enter(dsl_pool_t *dp, void *tag); +void dsl_pool_config_enter_prio(dsl_pool_t *dp, void *tag); void dsl_pool_config_exit(dsl_pool_t *dp, void *tag); boolean_t dsl_pool_config_held(dsl_pool_t *dp); boolean_t dsl_pool_config_held_writer(dsl_pool_t *dp); diff --git a/include/sys/rrwlock.h b/include/sys/rrwlock.h index 25c8a52467..d2bdff495c 100644 --- a/include/sys/rrwlock.h +++ b/include/sys/rrwlock.h @@ -72,6 +72,7 @@ void rrw_init(rrwlock_t *rrl, boolean_t track_all); void rrw_destroy(rrwlock_t *rrl); void rrw_enter(rrwlock_t *rrl, krw_t rw, void *tag); void rrw_enter_read(rrwlock_t *rrl, void *tag); +void rrw_enter_read_prio(rrwlock_t *rrl, void *tag); void rrw_enter_write(rrwlock_t *rrl); void rrw_exit(rrwlock_t *rrl, void *tag); boolean_t rrw_held(rrwlock_t *rrl, krw_t rw); diff --git a/module/zfs/dmu_objset.c b/module/zfs/dmu_objset.c index bc1aa12867..823a156777 100644 --- a/module/zfs/dmu_objset.c +++ b/module/zfs/dmu_objset.c @@ -1784,7 +1784,15 @@ dmu_objset_find_dp_cb(void *arg) dmu_objset_find_ctx_t *dcp = arg; dsl_pool_t *dp = dcp->dc_dp; - dsl_pool_config_enter(dp, FTAG); + /* + * We need to get a pool_config_lock here, as there are several + * asssert(pool_config_held) down the stack. Getting a lock via + * dsl_pool_config_enter is risky, as it might be stalled by a + * pending writer. This would deadlock, as the write lock can + * only be granted when our parent thread gives up the lock. + * The _prio interface gives us priority over a pending writer. + */ + dsl_pool_config_enter_prio(dp, FTAG); dmu_objset_find_dp_impl(dcp); diff --git a/module/zfs/dsl_pool.c b/module/zfs/dsl_pool.c index 5d804352dd..23cf438628 100644 --- a/module/zfs/dsl_pool.c +++ b/module/zfs/dsl_pool.c @@ -1050,6 +1050,13 @@ dsl_pool_config_enter(dsl_pool_t *dp, void *tag) rrw_enter(&dp->dp_config_rwlock, RW_READER, tag); } +void +dsl_pool_config_enter_prio(dsl_pool_t *dp, void *tag) +{ + ASSERT(!rrw_held(&dp->dp_config_rwlock, RW_READER)); + rrw_enter_read_prio(&dp->dp_config_rwlock, tag); +} + void dsl_pool_config_exit(dsl_pool_t *dp, void *tag) { diff --git a/module/zfs/rrwlock.c b/module/zfs/rrwlock.c index 8e80166c7d..29a22534e6 100644 --- a/module/zfs/rrwlock.c +++ b/module/zfs/rrwlock.c @@ -159,8 +159,8 @@ rrw_destroy(rrwlock_t *rrl) refcount_destroy(&rrl->rr_linked_rcount); } -void -rrw_enter_read(rrwlock_t *rrl, void *tag) +static void +rrw_enter_read_impl(rrwlock_t *rrl, boolean_t prio, void *tag) { mutex_enter(&rrl->rr_lock); #if !defined(DEBUG) && defined(_KERNEL) @@ -176,7 +176,7 @@ rrw_enter_read(rrwlock_t *rrl, void *tag) ASSERT(refcount_count(&rrl->rr_anon_rcount) >= 0); while (rrl->rr_writer != NULL || (rrl->rr_writer_wanted && - refcount_is_zero(&rrl->rr_anon_rcount) && + refcount_is_zero(&rrl->rr_anon_rcount) && !prio && rrn_find(rrl) == NULL)) cv_wait(&rrl->rr_cv, &rrl->rr_lock); @@ -191,6 +191,25 @@ rrw_enter_read(rrwlock_t *rrl, void *tag) mutex_exit(&rrl->rr_lock); } +void +rrw_enter_read(rrwlock_t *rrl, void *tag) +{ + rrw_enter_read_impl(rrl, B_FALSE, tag); +} + +/* + * take a read lock even if there are pending write lock requests. if we want + * to take a lock reentrantly, but from different threads (that have a + * relationship to each other), the normal detection mechanism to overrule + * the pending writer does not work, so we have to give an explicit hint here. + */ +void +rrw_enter_read_prio(rrwlock_t *rrl, void *tag) +{ + rrw_enter_read_impl(rrl, B_TRUE, tag); +} + + void rrw_enter_write(rrwlock_t *rrl) {