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From: Mark Johnston <markj@FreeBSD.org>
Date: Tue, 5 Jul 2016 17:59:04 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r302346 - head/sys/kern
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Author: markj
Date: Tue Jul  5 17:59:04 2016
New Revision: 302346
URL: https://svnweb.freebsd.org/changeset/base/302346

Log:
  Ensure that spinlock sections are balanced even after a panic.
  
  vpanic() uses spinlock_enter() to disable interrupts before dumping core.
  However, when the scheduler is stopped and INVARIANTS is not configured,
  thread_lock() does not acquire a spinlock section, while thread_unlock()
  releases one. This can result in interrupts staying enabled while the
  kernel dumps core, complicating post-mortem analysis of the crash.
  
  Approved by:	re (gjb)
  MFC after:	1 week
  Sponsored by:	EMC / Isilon Storage Division

Modified:
  head/sys/kern/kern_mutex.c

Modified: head/sys/kern/kern_mutex.c
==============================================================================
--- head/sys/kern/kern_mutex.c	Tue Jul  5 16:37:01 2016	(r302345)
+++ head/sys/kern/kern_mutex.c	Tue Jul  5 17:59:04 2016	(r302346)
@@ -657,8 +657,15 @@ thread_lock_flags_(struct thread *td, in
 	i = 0;
 	tid = (uintptr_t)curthread;
 
-	if (SCHEDULER_STOPPED())
+	if (SCHEDULER_STOPPED()) {
+		/*
+		 * Ensure that spinlock sections are balanced even when the
+		 * scheduler is stopped, since we may otherwise inadvertently
+		 * re-enable interrupts while dumping core.
+		 */
+		spinlock_enter();
 		return;
+	}
 
 #ifdef KDTRACE_HOOKS
 	spin_time -= lockstat_nsecs(&td->td_lock->lock_object);