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From: Fabien Thomas <fabient@FreeBSD.org>
Date: Tue, 27 Mar 2012 14:02:23 +0000 (UTC)
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Subject: svn commit: r233544 - head/sys/dev/hwpmc
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Author: fabient
Date: Tue Mar 27 14:02:22 2012
New Revision: 233544
URL: http://svn.freebsd.org/changeset/base/233544

Log:
  Fix random deadlock on pmcstat exit:
  - Exit the thread when soft shutdown is requested
  - Wakeup owner thread.
  
  Reproduced/tested by looping pmcstat measurement:
  pmcstat -S instructions -O/tmp/test ls
  
  MFC after:	1 week

Modified:
  head/sys/dev/hwpmc/hwpmc_logging.c

Modified: head/sys/dev/hwpmc/hwpmc_logging.c
==============================================================================
--- head/sys/dev/hwpmc/hwpmc_logging.c	Tue Mar 27 14:01:09 2012	(r233543)
+++ head/sys/dev/hwpmc/hwpmc_logging.c	Tue Mar 27 14:02:22 2012	(r233544)
@@ -285,6 +285,7 @@ pmclog_loop(void *arg)
 			if ((lb = TAILQ_FIRST(&po->po_logbuffers)) == NULL) {
 				mtx_unlock_spin(&po->po_mtx);
 
+				/* No more buffers and shutdown required. */
 				if (po->po_flags & PMC_PO_SHUTDOWN) {
 					mtx_unlock(&pmc_kthread_mtx);
 					/*
@@ -293,6 +294,7 @@ pmclog_loop(void *arg)
 					 */
 					fo_close(po->po_file, curthread);
 					mtx_lock(&pmc_kthread_mtx);
+					break;
 				}
 
 				(void) msleep(po, &pmc_kthread_mtx, PWAIT,
@@ -355,6 +357,7 @@ pmclog_loop(void *arg)
 		lb = NULL;
 	}
 
+	wakeup_one(po->po_kthread);
 	po->po_kthread = NULL;
 
 	mtx_unlock(&pmc_kthread_mtx);
@@ -653,8 +656,7 @@ pmclog_deconfigure_log(struct pmc_owner 
 	    ("[pmclog,%d] po=%p no log file", __LINE__, po));
 
 	/* stop the kthread, this will reset the 'OWNS_LOGFILE' flag */
-	if (po->po_kthread)
-		pmclog_stop_kthread(po);
+	pmclog_stop_kthread(po);
 
 	KASSERT(po->po_kthread == NULL,
 	    ("[pmclog,%d] po=%p kthread not stopped", __LINE__, po));