arc4rand may block once with the following non-sleepable locks held:
exclusive sleep mutex tcp_sc_head (tcp_sc_head) r = 0 (0xfffffe000077a0b0) locked @ /usr/home/conrad/src/freebsd/sys/netinet/tcp_syncache.c:531
stack backtrace:
#0 0xffffffff80c127a4 at witness_debugger.part.14+0xa4
#1 0xffffffff80c15aa5 at witness_warn+0x285
#2 0xffffffff80c93be1 at arc4rand+0x41
#3 0xffffffff80c93da8 at arc4random+0x18
#4 0xffffffff80de6b9d at syncache_add+0x6dd
#5 0xffffffff80dcd778 at tcp_input+0x1788
#6 0xffffffff80d443c0 at ip_input+0x170
#7 0xffffffff80cd0fb8 at netisr_dispatch_src+0x328
#8 0xffffffff80cb25be at ether_demux+0x1ae
#9 0xffffffff80cb318a at ether_nh_input+0x27a
#10 0xffffffff80cd0fb8 at netisr_dispatch_src+0x328
#11 0xffffffff80cb1fd4 at ether_input+0xa4
#12 0xffffffff809dcd6a at vtnet_rxq_eof+0x40a
#13 0xffffffff809dd16b at vtnet_rx_vq_intr+0x7b
#14 0xffffffff80b684be at ithread_loop+0x13e
// TCP initial send sequence number; see https://tools.ietf.org/html/rfc6528
// It seems like in the absense of an RNG, using a syncookie seems like a good
// fallback? Unique index + 1-way PRF (SipHash); just has to be good enough to
// be unpredictable in range [0,2^32].
Apr 19 21:03:05 testvm kernel: arc4rand may block once with the following non-sleepable locks held:
Apr 19 21:03:05 testvm kernel: exclusive sleep mutex isn_mtx (isn_mtx) r = 0 (0xffffffff8212d260) locked @ /usr/home/conrad/src/freebsd/sys/netinet/tcp_subr.c:2704
Apr 19 21:03:05 testvm kernel: exclusive rw tcpinp (tcpinp) r = 0 (0xfffff8000539d3f0) locked @ /usr/home/conrad/src/freebsd/sys/netinet/tcp_usrreq.c:533
Apr 19 21:03:05 testvm kernel: stack backtrace:
Apr 19 21:03:05 testvm kernel: #0 0xffffffff80c11f64 at witness_debugger.part.14+0xa4
Apr 19 21:03:05 testvm kernel: #1 0xffffffff80c15265 at witness_warn+0x285
Apr 19 21:03:05 testvm kernel: #2 0xffffffff80c93371 at arc4rand+0x41
Apr 19 21:03:05 testvm kernel: #3 0xffffffff80c93538 at arc4random+0x18
Apr 19 21:03:05 testvm kernel: #4 0xffffffff80de11d4 at tcp_new_isn+0xe4
Apr 19 21:03:05 testvm kernel: #5 0xffffffff80dec2db at tcp_connect+0x23b
Apr 19 21:03:05 testvm kernel: #6 0xffffffff80decc8f at tcp_usr_connect+0xbf
Apr 19 21:03:05 testvm kernel: #7 0xffffffff80c454e8 at soconnectat.part.16+0x118
Apr 19 21:03:05 testvm kernel: #8 0xffffffff80e731c7 at clnt_vc_create+0x137
Apr 19 21:03:05 testvm kernel: #9 0xffffffff80e7115f at clnt_reconnect_call+0x6af
Apr 19 21:03:05 testvm kernel: #10 0xffffffff80a49d97 at newnfs_request+0x847
Apr 19 21:03:05 testvm kernel: #11 0xffffffff80a76aea at nfsrpc_getattrnovp+0xca
Apr 19 21:03:05 testvm kernel: #12 0xffffffff80a9cec4 at mountnfs+0x674
Apr 19 21:03:05 testvm kernel: #13 0xffffffff80a9ecc6 at nfs_mount+0x1966
Apr 19 21:03:05 testvm kernel: #14 0xffffffff80c70388 at vfs_mount_sigdefer+0x28
Apr 19 21:03:05 testvm kernel: #15 0xffffffff80c75cb0 at vfs_domount+0x570
Apr 19 21:03:05 testvm kernel: #16 0xffffffff80c7695b at vfs_donmount+0x30b
Apr 19 21:03:05 testvm kernel: #17 0xffffffff80c76f06 at sys_nmount+0x76