5981 Deadlock in dmu_objset_find_dp
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Dan McDonald <danmcd@omniti.com>
Approved by: Robert Mustacchi <rm@joyent.com>
References:
https://www.illumos.org/issues/5981
https://github.com/illumos/illumos-gate/commit/
1d3f896
Ported-by: kernelOfTruth kerneloftruth@gmail.com
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #3553
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);
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);
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);
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)
{
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)
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);
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)
{