5981 Deadlock in dmu_objset_find_dp

*** 157,168 ****
          ASSERT(rrl->rr_writer == NULL);
          refcount_destroy(&rrl->rr_anon_rcount);
          refcount_destroy(&rrl->rr_linked_rcount);
  }
  
! void
! rrw_enter_read(rrwlock_t *rrl, void *tag)
  {
          mutex_enter(&rrl->rr_lock);
  #if !defined(DEBUG) && defined(_KERNEL)
          if (rrl->rr_writer == NULL && !rrl->rr_writer_wanted &&
              !rrl->rr_track_all) {
--- 157,168 ----
          ASSERT(rrl->rr_writer == NULL);
          refcount_destroy(&rrl->rr_anon_rcount);
          refcount_destroy(&rrl->rr_linked_rcount);
  }
  
! static void
! rrw_enter_read_impl(rrwlock_t *rrl, boolean_t prio, void *tag)
  {
          mutex_enter(&rrl->rr_lock);
  #if !defined(DEBUG) && defined(_KERNEL)
          if (rrl->rr_writer == NULL && !rrl->rr_writer_wanted &&
              !rrl->rr_track_all) {
*** 174,184 ****
  #endif
          ASSERT(rrl->rr_writer != curthread);
          ASSERT(refcount_count(&rrl->rr_anon_rcount) >= 0);
  
          while (rrl->rr_writer != NULL || (rrl->rr_writer_wanted &&
!             refcount_is_zero(&rrl->rr_anon_rcount) &&
              rrn_find(rrl) == NULL))
                  cv_wait(&rrl->rr_cv, &rrl->rr_lock);
  
          if (rrl->rr_writer_wanted || rrl->rr_track_all) {
                  /* may or may not be a re-entrant enter */
--- 174,184 ----
  #endif
          ASSERT(rrl->rr_writer != curthread);
          ASSERT(refcount_count(&rrl->rr_anon_rcount) >= 0);
  
          while (rrl->rr_writer != NULL || (rrl->rr_writer_wanted &&
!             refcount_is_zero(&rrl->rr_anon_rcount) && !prio &&
              rrn_find(rrl) == NULL))
                  cv_wait(&rrl->rr_cv, &rrl->rr_lock);
  
          if (rrl->rr_writer_wanted || rrl->rr_track_all) {
                  /* may or may not be a re-entrant enter */
*** 190,199 ****
--- 190,218 ----
          ASSERT(rrl->rr_writer == NULL);
          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)
  {
          mutex_enter(&rrl->rr_lock);
          ASSERT(rrl->rr_writer != curthread);