- Fix the kthread_{suspend, resume, suspend_check}() locking.

  In the current code, the locking is completely broken and may lead
  easilly to deadlocks. Fix it by using the proc_mtx, linked to the
  suspending thread, as lock for the operation.  Keep using the
  thread_lock for setting and reading the flag even if it is not entirely
  necessary (atomic ops may do it as well, but this way the code is more
  readable).
- Fix a deadlock within kthread_suspend().
  The suspender should not sleep on a different channel wrt the suspended
  thread, or, otherwise, the awaker should wakeup both. Uniform the
  interface to what the kproc_* counterparts do (sleeping on the same
  channel).
- Change the kthread_suspend_check() prototype.
  kthread_suspend_check() always assumes curthread and must only refer to
  it, so skip the thread pointer as it may be easilly mistaken.
  If curthread is not a kthread, the system will panic.

In collabouration with:	jhb
Tested by:		Giovanni Trematerra
			<giovanni dot trematerra at gmail dot com>
MFC:			2 weeks

1 files changed, 4 insertions, 7 deletions

diff --git a/share/man/man9/kthread.9 b/share/man/man9/kthread.9
index ffb5179..d2c770b 100644
--- a/share/man/man9/kthread.9
+++ b/share/man/man9/kthread.9
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd January 26, 2009
+.Dd January 24, 2010
 .Dt KTHREAD 9
 .Os
 .Sh NAME
@@ -50,7 +50,7 @@
 .Ft int
 .Fn kthread_suspend "struct thread *td" "int timo"
 .Ft void
-.Fn kthread_suspend_check "struct thread *td"
+.Fn kthread_suspend_check "void"
 .In sys/unistd.h
 .Ft int
 .Fo kthread_add
@@ -208,12 +208,9 @@ functions are used to suspend and resume a kernel thread.
 During the main loop of its execution, a kernel thread that wishes to allow
 itself to be suspended should call
 .Fn kthread_suspend_check
-passing in
-.Va curthread
-as the only argument.
-This function checks to see if the kernel thread has been asked to suspend.
+in order to check if the it has been asked to suspend.
 If it has, it will
-.Xr tsleep 9
+.Xr msleep 9
 until it is told to resume.
 Once it has been told to resume it will return allowing execution of the
 kernel thread to continue.