svn commit: r286880 - head/sys/kern

[Julien Charbon]

Author: jch
Date: Tue Aug 18 10:15:09 2015
New Revision: 286880
URL: https://svnweb.freebsd.org/changeset/base/286880

Log:
  callout_stop() should return 0 (fail) when the callout is currently
  being serviced and indeed unstoppable.
  
  A scenario to reproduce this case is:
  
  - the callout is being serviced and at same time,
  - callout_reset() is called on this callout that sets
    the CALLOUT_PENDING flag and at same time,
  - callout_stop() is called on this callout and returns 1 (success)
    even if the callout is indeed currently running and unstoppable.
  
  This issue was caught up while making r284245 (D2763) workaround, and
  was discussed at BSDCan 2015.  Once applied the r284245 workaround
  is not needed anymore and will be reverted.
  
  Differential Revision:	https://reviews.freebsd.org/D3078
  Reviewed by:		jhb
  Sponsored by:		Verisign, Inc.

Modified:
  head/sys/kern/kern_timeout.c

Modified: head/sys/kern/kern_timeout.c
==============================================================================
--- head/sys/kern/kern_timeout.c	Tue Aug 18 10:07:03 2015	(r286879)
+++ head/sys/kern/kern_timeout.c	Tue Aug 18 10:15:09 2015	(r286880)
@@ -1150,7 +1150,7 @@ _callout_stop_safe(struct callout *c, in
 	struct callout_cpu *cc, *old_cc;
 	struct lock_class *class;
 	int direct, sq_locked, use_lock;
-	int not_on_a_list;
+	int not_on_a_list, not_running;
 
 	if (safe)
 		WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, c->c_lock,
@@ -1378,8 +1378,15 @@ again:
 		}
 	}
 	callout_cc_del(c, cc);
+
+	/*
+	 * If we are asked to stop a callout which is currently in progress
+	 * and indeed impossible to stop then return 0.
+	 */
+	not_running = !(cc_exec_curr(cc, direct) == c);
+
 	CC_UNLOCK(cc);
-	return (1);
+	return (not_running);
 }
 
 void