svn commit: r333758 - head/sys/kern

[Matt Macy]

Author: mmacy
Date: Thu May 17 19:41:58 2018
New Revision: 333758
URL: https://svnweb.freebsd.org/changeset/base/333758

Log:
  epoch(9): fix potential deadlock
  
  Don't acquire a waiting thread's lock while holding our own
  
  Approved by:	sbruno

Modified:
  head/sys/kern/subr_epoch.c

Modified: head/sys/kern/subr_epoch.c
==============================================================================
--- head/sys/kern/subr_epoch.c	Thu May 17 19:30:57 2018	(r333757)
+++ head/sys/kern/subr_epoch.c	Thu May 17 19:41:58 2018	(r333758)
@@ -407,9 +407,13 @@ epoch_block_handler(struct ck_epoch *global __unused, 
 		 * restore on exit from epoch_wait().
 		 */
 		if (!TD_IS_INHIBITED(tdwait) && tdwait->td_priority > td->td_priority) {
+			critical_enter();
+			thread_unlock(td);
 			thread_lock(tdwait);
 			sched_prio(tdwait, td->td_priority);
 			thread_unlock(tdwait);
+			thread_lock(td);
+			critical_exit();
 		}
 		if (TD_IS_INHIBITED(tdwait) && TD_ON_LOCK(tdwait) &&
 			((ts = tdwait->td_blocked) != NULL)) {