t: FAILED: copy_blocks/283: rfd == -1


(gdb) where
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
#1  0x00007fce4e595801 in __GI_abort () at abort.c:79
#2  0x0000564f573183e8 in testutil_die (e=0, fmt=0x564f57533227 "%s/%d: %s") at misc.c:66
#3  0x0000564f573038af in copy_blocks (session=0x564f584d0db8, bkup_c=0x7fce2c00ad00, 
    name=0x7fce2c00a030 "WiredTigerHS.wt") at backup.c:283
#4  0x0000564f573043ce in backup (arg=0x0) at backup.c:460
#5  0x00007fce4e94d6db in start_thread (arg=0x7fce33fff700) at pthread_create.c:463
#6  0x00007fce4e67688f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95