linux-kernel - [PATCH ver 2] Add kerneldoc for flush_scheduled

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Message-ID: <Pine.LNX.4.44L0.0908121154370.9635-100000@iolanthe.rowland.org>
Date:	Wed, 12 Aug 2009 11:56:35 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Randy Dunlap <randy.dunlap@...cle.com>
Subject: [PATCH ver 2] Add kerneldoc for flush_scheduled_work()

This patch (as1279b) adds kerneldoc for flush_scheduled_work()
containing a stern warning that the function should be avoided.

Signed-off-by: Alan Stern <stern@...land.harvard.edu>

---

Version 2: Body text reformatted to use consistent line lengths.  
Kerneldoc requires the short description to occupy a single line, so 
the first line of the comment cannot be broken.


Index: usb-2.6/kernel/workqueue.c
===================================================================
--- usb-2.6.orig/kernel/workqueue.c
+++ usb-2.6/kernel/workqueue.c
@@ -739,6 +739,26 @@ int schedule_on_each_cpu(work_func_t fun
 	return 0;
 }
 
+/**
+ * flush_scheduled_work - ensure that all work scheduled on keventd_wq has run to completion.
+ *
+ * Blocks until all works on the keventd_wq global workqueue have
+ * completed.  We sleep until all works present upon entry have been
+ * handled, but we are not livelocked by new incoming ones.
+ * 
+ * Use of this function is discouraged, as it is highly prone to
+ * deadlock.  It should never be called from within a work routine
+ * on the global queue, and it should never be called while holding
+ * a mutex required by one of the works on the global queue.  But
+ * the fact that keventd_wq _is_ global means that it can contain
+ * works requiring practically any mutex.  Hence this routine
+ * shouldn't be called while holding any mutex.
+ * 
+ * Consider using cancel_work_sync() or cancel_delayed_work_sync()
+ * instead.  They don't do the same thing (they cancel the work
+ * instead of waiting for it to complete), but in most cases they
+ * will suffice.
+ */
 void flush_scheduled_work(void)
 {
 	flush_workqueue(keventd_wq);

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