svn commit: r185116 - user/lstewart/misc_7.x/sys/kern

[Lawrence Stewart]

Author: lstewart
Date: Thu Nov 20 04:04:22 2008
New Revision: 185116
URL: http://svn.freebsd.org/changeset/base/185116

Log:
  Fix a bug in kthread_exit() which led to potential deadlock in code that
  was relying on the documented behaviour in the kthread(9) man page. This brings
  the wakeup() related behaviour of kthread_exit in 7.x inline with 8.x.
  
  I've tested the fix with a simple scenario that was previously deadlocking. A
  waiting thread waits on a terminating thread by calling mtx_sleep() with the
  "chan" argument set to the *thread obtained by calling
  FIRST_THREAD_IN_PROC(*proc_that_will_exit).
  
  Without this patch, the waiting thread never gets woken because kthread_exit()
  calls wakeup() on the *proc. With this patch, the wait thread gets woken and
  all is good in the world again.
  
  For more details, refer to:
  http://lists.freebsd.org/pipermail/freebsd-arch/2008-November/008688.html
  
  Discussed with:	attilio@, julian@

Modified:
  user/lstewart/misc_7.x/sys/kern/kern_kthread.c

Modified: user/lstewart/misc_7.x/sys/kern/kern_kthread.c
==============================================================================
--- user/lstewart/misc_7.x/sys/kern/kern_kthread.c	Thu Nov 20 03:34:36 2008	(r185115)
+++ user/lstewart/misc_7.x/sys/kern/kern_kthread.c	Thu Nov 20 04:04:22 2008	(r185116)
@@ -144,6 +144,7 @@ kthread_exit(int ecode)
 	 * Wakeup anyone waiting for us to exit.
 	 */
 	wakeup(p);
+	wakeup(td);
 
 	/* Buh-bye! */
 	exit1(td, W_EXITCODE(ecode, 0));