panic: Memory modified after free

[Yuri Pankov]

(posting to fs@ as backtrace suggests zfs)

Started seeing the following panic (sometimes reproducible, so can't point specific revision or time range) untaring an archive over ssh into my home directory on zfs:

panic: Memory modified after free 0xfffff80404cff000(4096) val=dead40de @ 0xfffff80404cff694

cpuid = 4
time = 1570493241
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe00df912650
vpanic() at vpanic+0x19d/frame 0xfffffe00df9126a0
panic() at panic+0x43/frame 0xfffffe00df912700
trash_ctor() at trash_ctor+0x49/frame 0xfffffe00df912710
uma_zalloc_arg() at uma_zalloc_arg+0xa24/frame 0xfffffe00df9127a0
abd_alloc() at abd_alloc+0x152/frame 0xfffffe00df9127f0
arc_hdr_alloc_pabd() at arc_hdr_alloc_pabd+0x166/frame 0xfffffe00df912820
arc_write_ready() at arc_write_ready+0x463/frame 0xfffffe00df912860
zio_ready() at zio_ready+0xde/frame 0xfffffe00df9128a0
zio_execute() at zio_execute+0x17c/frame 0xfffffe00df9128e0
taskqueue_run_locked() at taskqueue_run_locked+0x10c/frame 0xfffffe00df912940
taskqueue_thread_loop() at taskqueue_thread_loop+0x88/frame 0xfffffe00df912970
fork_exit() at fork_exit+0x84/frame 0xfffffe00df9129b0
fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe00df9129b0
--- trap 0, rip = 0, rsp = 0, rbp = 0 ---

Full text dump is at https://people.freebsd.org/~yuripv/core.txt.0.

Real problem or failing hardware (memory?)?