[Bug 219846] [panic] [kevent] mutex nm_kn_lock not owned, netmap with INVARIANTS+WITNESS

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=219846

--- Comment #6 from Aleksandr Fedorov <aleksandr.fedorov at itglobal.com> ---
This patch fix the panic:

Index: sys/dev/netmap/netmap_freebsd.c
===================================================================
--- sys/dev/netmap/netmap_freebsd.c     (revision 342550)
+++ sys/dev/netmap/netmap_freebsd.c     (working copy)
@@ -1321,7 +1321,12 @@
        /* use a non-zero hint to tell the notification from the
         * call done in kqueue_scan() which uses 0
         */
-       KNOTE_UNLOCKED(&si->si.si_note, 0x100 /* notification */);
+
+       if (mtx_owned(&si->m)) {
+               KNOTE_LOCKED(&si->si.si_note, 0x100 /* notification */);
+       } else {
+               KNOTE_UNLOCKED(&si->si.si_note, 0x100 /* notification */);
+       }
 }

 void

It seems there are several paths to call the function nm_os_selwakeup():

Trace from bhyve:
dtrace: script './nm_os_selwakeup.d' matched 1 probe
CPU     ID                    FUNCTION:NAME
 18  39521            nm_os_selwakeup:entry
              kernel`netmap_notify+0x1d
              kernel`nm_vale_flush+0xb70
              kernel`netmap_vale_vp_txsync+0x51d
              kernel`netmap_ioctl+0x4e1
              kernel`freebsd_netmap_ioctl+0x88
              kernel`devfs_ioctl+0xca
              kernel`VOP_IOCTL_APV+0x63
              kernel`vn_ioctl+0x124
              kernel`devfs_ioctl_f+0x1f
              kernel`kern_ioctl+0x29b
              kernel`sys_ioctl+0x15d
              kernel`amd64_syscall+0x276
              kernel`0xffffffff8107a81d


 20  39521            nm_os_selwakeup:entry
              kernel`netmap_notify+0x1d
              kernel`netmap_poll+0x5e6
              kernel`netmap_knrw+0x6f
              kernel`kqueue_kevent+0x56d
              kernel`kern_kevent_fp+0x97
              kernel`kern_kevent+0x9f
              kernel`kern_kevent_generic+0x70
              kernel`sys_kevent+0x61
              kernel`amd64_syscall+0x276
              kernel`0xffffffff8107a81d

The first does not hold the mutex ("nm_kn_lock"), the second does.

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