panic: APIC: Previous IPI is stuck

with a most recent -GENERIC current, on an SMP machine :

panic: APIC: Previous IPI is stuck
cpuid = 1
KDB: enter: panic
[thread pid 88971 tid 100050 ]
Stopped at      kdb_enter+0x2b: nop
db> where
Tracing pid 88971 tid 100050 td 0xc134b600
kdb_enter(c0857f0a) at kdb_enter+0x2b
panic(c087bf1e,1,c66a1000,c725ea28,c07e7f91) at panic+0x127
lapic_ipi_vectored(f4,fffffffd,c725ea38,c07e7c89,f4) at 
lapic_ipi_vectored+0x93
ipi_all_but_self(f4) at ipi_all_but_self+0xd
smp_tlb_shootdown(f4,c66a1000,0) at smp_tlb_shootdown+0x49
smp_invlpg(c66a1000) at smp_invlpg+0x1b
pmap_invalidate_page(c09a1100,c66a1000) at pmap_invalidate_page+0x6c
pmap_remove_pte(c09a1100,bff19a84,c66a1000) at pmap_remove_pte+0x5a
pmap_remove(c09a1100,c66a1000,c66a5000) at pmap_remove+0x10e
vm_map_delete(c1042000,c66a1000,c66a5000,c1767990,c1767990) at 
vm_map_delete+0x159
vm_map_remove(c1042000,c66a1000,c66a5000,c1767990,c725eb30) at 
vm_map_remove+0x42
pipe_free_kmem(c1767990,c1767b00,0,c085c3ca,5ea) at pipe_free_kmem+0x51
pipeclose(c1767990,c1767a30,c160b360,c725eb5c,c06173cc) at pipeclose+0x331
pipe_close(c160b360,c134b600) at pipe_close+0x2a
fdrop_locked(c160b360,c134b600,c124f9a0,0,c0854d6c) at fdrop_locked+0x88
fdrop(c160b360,c134b600,c725eba8,c0653b7c,c0854d6c) at fdrop+0x24
closef(c160b360,c134b600) at closef+0x35f
fdfree(c134b600,c1349358,0,c085b878,6ac) at fdfree+0x473
exit1(c134b600,0,c725ed30,c07efcfb,c134b600) at exit1+0x3f6

	KGDB trace to follow

	TfH