The umtx_lock mutex is used by top-half of the kernel, but is

currently a spin lock.  Apparently, the only reason for this is that
umtx_thread_exit() is called under the process spinlock, which put the
requirement on the umtx_lock.  Note that the witness static order list
is wrong for the umtx_lock, umtx_lock is explicitely before any thread
lock, so it is also before sleepq locks.

Change umtx_lock to be the sleepable mutex.  For the reason above, the
calls to umtx_thread_exit() are moved from thread_exit() earlier in
each caller, when the process spin lock is not yet taken.

Discussed with:	jhb
Tested by:	pho (previous version)
Sponsored by:	The FreeBSD Foundation
MFC after:	3 weeks

1 files changed, 2 insertions, 0 deletions

diff --git a/sys/kern/kern_kthread.c b/sys/kern/kern_kthread.c
index 969c513eb8fe..ee94de0e78a5 100644
--- a/sys/kern/kern_kthread.c
+++ b/sys/kern/kern_kthread.c
@@ -38,6 +38,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/rwlock.h>
 #include <sys/signalvar.h>
 #include <sys/sx.h>
+#include <sys/umtx.h>
 #include <sys/unistd.h>
 #include <sys/wait.h>
 #include <sys/sched.h>
@@ -339,6 +340,7 @@ kthread_exit(void)
 	}
 	LIST_REMOVE(curthread, td_hash);
 	rw_wunlock(&tidhash_lock);
+	umtx_thread_exit(curthread);
 	PROC_SLOCK(p);
 	thread_exit();
 }