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, 5 insertions, 1 deletions

diff --git a/sys/kern/subr_witness.c b/sys/kern/subr_witness.c
index 518fb492b075..f80026a32d43 100644
--- a/sys/kern/subr_witness.c
+++ b/sys/kern/subr_witness.c
@@ -492,6 +492,11 @@ static struct witness_order_list_entry order_lists[] = {
 	{ "time lock", &lock_class_mtx_sleep },
 	{ NULL, NULL },
 	/*
+	 * umtx
+	 */
+	{ "umtx lock", &lock_class_mtx_sleep },
+	{ NULL, NULL },
+	/*
 	 * Sockets
 	 */
 	{ "accept", &lock_class_mtx_sleep },
@@ -637,7 +642,6 @@ static struct witness_order_list_entry order_lists[] = {
 #endif
 	{ "process slock", &lock_class_mtx_spin },
 	{ "sleepq chain", &lock_class_mtx_spin },
-	{ "umtx lock", &lock_class_mtx_spin },
 	{ "rm_spinlock", &lock_class_mtx_spin },
 	{ "turnstile chain", &lock_class_mtx_spin },
 	{ "turnstile lock", &lock_class_mtx_spin },