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From: Konstantin Belousov <kib@FreeBSD.org>
Date: Wed, 9 Nov 2011 17:15:51 +0000 (UTC)
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Subject: svn commit: r227393 - head/sys/fs/procfs
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Author: kib
Date: Wed Nov  9 17:15:51 2011
New Revision: 227393
URL: http://svn.freebsd.org/changeset/base/227393

Log:
  Lock the thread lock around block that retrieves td_wmesg. Otherwise,
  procfs could see a thread with assigned td_wchan but still NULL td_wmesg.
  
  Reported and tested by:	pho
  MFC after:	1 week

Modified:
  head/sys/fs/procfs/procfs_status.c

Modified: head/sys/fs/procfs/procfs_status.c
==============================================================================
--- head/sys/fs/procfs/procfs_status.c	Wed Nov  9 17:13:41 2011	(r227392)
+++ head/sys/fs/procfs/procfs_status.c	Wed Nov  9 17:15:51 2011	(r227393)
@@ -113,12 +113,14 @@ procfs_doprocstatus(PFS_FILL_ARGS)
 	}
 
 	tdfirst = FIRST_THREAD_IN_PROC(p);
+	thread_lock(tdfirst);
 	if (tdfirst->td_wchan != NULL) {
 		KASSERT(tdfirst->td_wmesg != NULL,
 		    ("wchan %p has no wmesg", tdfirst->td_wchan));
 		wmesg = tdfirst->td_wmesg;
 	} else
 		wmesg = "nochan";
+	thread_unlock(tdfirst);
 
 	if (p->p_flag & P_INMEM) {
 		struct timeval start, ut, st;