panic: non-kernel pmap pmap ADDR cpu 0 pcid 0

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: c93a14fd tail: fix the checks if the file was rotated
git tree: freebsd
console output: https://syzkaller.appspot.com/x/log.txt?x=117fbae1a00000
dashboard link: https://syzkaller.appspot.com/bug?extid=20d547cafb8176ad5d45
userspace arch: i386
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=162f8066a00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+20d547...@syzkaller.appspotmail.com

#4 0xffffffff816aapanic: non-kernel pmap pmap 0xfffff8000b2d8130 cpu 0 pcid
0
cpuid = 0
time = 1560160392
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x47/frame
0xfffffe0020ed1368
vpanic() at vpanic+0x1e0/frame 0xfffffe0020ed13c8
panic() at panic+0x43/frame 0xfffffe0020ed1428
pmap_pcid_alloc_checked() at pmap_pcid_alloc_checked+0x222/frame
0xfffffe0020ed1478
pmap_activate_sw_pcid_invpcid_pti() at
pmap_activate_sw_pcid_invpcid_pti+0x2b/frame 0xfffffe0020ed14d8
pmap_activate_sw() at pmap_activate_sw+0x78/frame 0xfffffe0020ed1528
ctx_switch_xsave() at ctx_switch_xsave+0x18/frame 0xfffffe0020ed1620
mi_switch() at mi_switch+0x22f/frame 0xfffffe0020ed1660
sleepq_switch() at sleepq_switch+0x17d/frame 0xfffffe0020ed16b0
sleepq_catch_signals() at sleepq_catch_signals+0x55d/frame
0xfffffe0020ed1720
sleepq_wait_sig() at sleepq_wait_sig+0x24/frame 0xfffffe0020ed1760
_sleep() at _sleep+0x3c9/frame 0xfffffe0020ed1810
umtxq_sleep() at umtxq_sleep+0x205/frame 0xfffffe0020ed1880
do_wait() at do_wait+0x344/frame 0xfffffe0020ed1910
__umtx_op_wait_uint_private_compat32() at
__umtx_op_wait_uint_private_compat32+0x91/frame 0xfffffe0020ed1970
ia32_syscall() at ia32_syscall+0x452/frame 0xfffffe0020ed1ab0
int0x80_syscall_common() at int0x80_syscall_common+0x9c/frame 0xfbfdbf04
KDB: enter: panic
[ thread pid 787 tid 100116 ]
Stopped at kdb_enter+0x6a: movq $0,kdb_why


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