syzbot

panic: kernel diagnostic assertion "refs != ~0" failed: file "/syzkaller/managers/multicore/kernel/sys/kern/kern_synch.c", line 959
Stopped at      db_enter+0x25:  addq    $0x8,%rsp
    TID    PID    UID     PRFLAGS     PFLAGS  CPU  COMMAND
 307745  57371      0           0          0    0  syz-executor
db_enter() at db_enter+0x25 sys/arch/amd64/amd64/db_interface.c:438
panic(ffffffff834be3aa) at panic+0x1e5 sys/kern/subr_prf.c:198
__assert(ffffffff834f98d9,ffffffff835044e8,3bf,ffffffff8352cc4c) at __assert+0x29 sys/kern/subr_prf.c:-1
refcnt_finalize(ffff80003c3cb770,ffffffff834b50b0) at refcnt_finalize+0x1e7 sys/kern/kern_synch.c:960
pppx_if_destroy(0,ffff80003c3cb768) at pppx_if_destroy+0x3d sys/net/if_pppx.c:794
pppxclose(205b9a,1,2000,ffff80003c3c6560) at pppxclose+0xa0 sys/net/if_pppx.c:541
spec_close(ffff80003b7b2b10) at spec_close+0x417 sys/kern/spec_vnops.c:-1
VOP_CLOSE(fffff9006b6e6a80,1,fffff900097fd270,ffff80003c3c6560) at VOP_CLOSE+0x132 sys/kern/vfs_vops.c:156
vn_closefile(fffff9006a35f2c0,ffff80003c3c6560) at vn_closefile+0x12b vn_close sys/kern/vfs_vnops.c:298 [inline]
vn_closefile(fffff9006a35f2c0,ffff80003c3c6560) at vn_closefile+0x12b sys/kern/vfs_vnops.c:621
fdrop(fffff9006a35f2c0,ffff80003c3c6560) at fdrop+0x121 sys/kern/kern_descrip.c:1281
closef(fffff9006a35f2c0,ffff80003c3c6560) at closef+0x192 sys/kern/kern_descrip.c:1265
fdfree(ffff80003c3c6560) at fdfree+0x116 sys/kern/kern_descrip.c:1196
exit1(ffff80003c3c6560,0,0,1) at exit1+0x576 sys/kern/kern_exit.c:215
sys_exit(ffff80003c3c6560,ffff80003b7b2e80,ffff80003b7b2dd0) at sys_exit+0x1a sys/kern/kern_exit.c:-1
end trace frame: 0xffff80003b7b2e70, count: 0
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reports.  Insufficient info makes it difficult to find and fix bugs.
ddb{1}> 
ddb{1}> set $lines = 0
ddb{1}> set $maxwidth = 0
ddb{1}> show panic
*cpu1: kernel diagnostic assertion "refs != ~0" failed: file "/syzkaller/managers/multicore/kernel/sys/kern/kern_synch.c", line 959
ddb{1}>