With the following portal.conf:

 # cat portal.conf
 e/      rfilter e/      echo %s

...then mounting it:

 # mount_portal /tmp/m/portal.conf /tmp/m/p

...attaching gdb(1) to it:

 # gdb -p `pgrep mount_portal`
 GNU gdb (GDB) 8.0.1
 [...]
 (gdb) b portal_node_reclaim
 Breakpoint 1 at 0x1aa403040: file /usr/src/sbin/mount_portal/puffs_portal.c, line 805.
 (gdb) c
 Continuing.
 [Switching to LWP 1 of process 29602]

...and then doing:

 % head -1 /tmp/m/p/e/bar

Leads to:

 Thread 1 "" hit Breakpoint 1, portal_node_reclaim (pu=0x7ed8ec7ab000, opc=0x7ed8ec7b7020)
     at /usr/src/sbin/mount_portal/puffs_portal.c:805
 805     {
 (gdb) bt
 #0  portal_node_reclaim (pu=0x7ed8ec7ab000, opc=0x7ed8ec7b7020) at /usr/src/sbin/mount_portal/puffs_portal.c:805
 #1  0x00000001aa403528 in portal_node_getattr (pu=0x7ed8ec7ab000, opc=0x7ed8ec7b7020, va=0x7ed8ec7aa090, pcr=0x7ed8ec7aa038)
     at /usr/src/sbin/mount_portal/puffs_portal.c:593
 #2  0x00007ed8ec008d50 in dispatch (pcc=pcc@entry=0x7ed8ec740000) at /usr/src/lib/libpuffs/dispatcher.c:483
 #3  0x00007ed8ec009495 in puffs__ml_dispatch (pu=0x7ed8ec7ab000, pb=0x7ed8ec795050) at /usr/src/lib/libpuffs/dispatcher.c:64
 #4  0x00007ed8ec00b90e in puffs__framev_input (pu=pu@entry=0x7ed8ec7ab000, fctrl=0x7ed8ec7ab5f8, fio=fio@entry=0x7ed8ec79d060)
     at /usr/src/lib/libpuffs/framebuf.c:699
 #5  0x00007ed8ec00d80b in puffs__theloop (pcc=<optimized out>) at /usr/src/lib/libpuffs/puffs.c:909
 #6  0x00007ed8eb86b3a0 in ?? () from /lib/libc.so.12
 Backtrace stopped: Cannot access memory at address 0x7ed8ec780000
 (gdb) c
 Continuing.
 
 Thread 1 "" hit Breakpoint 1, portal_node_reclaim (pu=0x7ed8ec7ab000, opc=0x7ed8ec7b7020)
     at /usr/src/sbin/mount_portal/puffs_portal.c:805
 805     {
 (gdb) bt
 #0  portal_node_reclaim (pu=0x7ed8ec7ab000, opc=0x7ed8ec7b7020) at /usr/src/sbin/mount_portal/puffs_portal.c:805
 #1  0x00007ed8ec008e3b in dispatch (pcc=pcc@entry=0x7ed8ec740000) at /usr/src/lib/libpuffs/dispatcher.c:876
 #2  0x00007ed8ec009495 in puffs__ml_dispatch (pu=0x7ed8ec7ab000, pb=0x7ed8ec795050) at /usr/src/lib/libpuffs/dispatcher.c:64
 #3  0x00007ed8ec00b90e in puffs__framev_input (pu=pu@entry=0x7ed8ec7ab000, fctrl=0x7ed8ec7ab5f8, fio=fio@entry=0x7ed8ec79d060)
     at /usr/src/lib/libpuffs/framebuf.c:699
 #4  0x00007ed8ec00d80b in puffs__theloop (pcc=<optimized out>) at /usr/src/lib/libpuffs/puffs.c:909
 #5  0x00007ed8eb86b3a0 in ?? () from /lib/libc.so.12
 Backtrace stopped: Cannot access memory at address 0x7ed8ec780000
 (gdb) c
 Continuing.
 <jemalloc>: /usr/src/external/bsd/jemalloc/lib/../dist/src/rtree.c:205: Failed assertion: "!dependent || leaf != NULL"
 
 Thread 1 "" received signal SIGABRT, Aborted.
 0x00007ed8eb9a4f9a in _lwp_kill () from /lib/libc.so.12
 (gdb) bt
 #0  0x00007ed8eb9a4f9a in _lwp_kill () from /lib/libc.so.12
 #1  0x00007ed8eb9a4bc7 in abort () at /usr/src/lib/libc/stdlib/abort.c:74
 #2  0x00007ed8eb8de8f2 in rtree_child_leaf_tryread (elm=<optimized out>, dependent=<optimized out>)
     at /usr/src/external/bsd/jemalloc/lib/../dist/src/rtree.c:205
 #3  0x00007ed8eb8deb9c in je_rtree_leaf_elm_lookup_hard (tsdn=<optimized out>, rtree=0x7ed8ebc1d6a0 <je_extents_rtree>,
     rtree_ctx=0x7ed8ec7c6068, rtree_ctx@entry=0x7ed8ec77fe04, key=6510615555426900570, key@entry=139470145322456,
     dependent=dependent@entry=true, init_missing=init_missing@entry=false)
     at /usr/src/external/bsd/jemalloc/lib/../dist/src/rtree.c:292
 #4  0x00007ed8eb932f5b in rtree_leaf_elm_lookup (rtree=<optimized out>, init_missing=false, dependent=true,
     key=key@entry=139470145322456, rtree_ctx=rtree_ctx@entry=0x7ed8ec77fe04, tsdn=tsdn@entry=0x7ed8ec77fddc)
     at /usr/src/external/bsd/jemalloc/lib/../include/jemalloc/internal/rtree.h:381
 #5  rtree_read (rtree=<optimized out>, dependent=true, key=key@entry=139470145322456, rtree_ctx=rtree_ctx@entry=0x7ed8ec77fe04,
     tsdn=tsdn@entry=0x7ed8ec77fddc) at /usr/src/external/bsd/jemalloc/lib/../include/jemalloc/internal/rtree.h:406
 #6  rtree_szind_slab_read (tsdn=tsdn@entry=0x7ed8ec7c6040, rtree_ctx=rtree_ctx@entry=0x7ed8ec7c6068,
     key=key@entry=6510615555426900570, r_szind=r_szind@entry=0x7ed8ec77fdd8, r_slab=r_slab@entry=0x7ed8ec77fddc, dependent=true,
     rtree=<optimized out>) at /usr/src/external/bsd/jemalloc/lib/../include/jemalloc/internal/rtree.h:458
 #7  0x00007ed8eb9368c6 in ifree (tsd=0x7ed8ec7c6040, ptr=0x5a5a5a5a5a5a5a5a, tcache=0x7ed8ec7c6200, slow_path=<optimized out>)
     at /usr/src/external/bsd/jemalloc/lib/../dist/src/jemalloc.c:2239
 #8  0x00007ed8eb93a255 in free (ptr=0x5a5a5a5a5a5a5a5a) at /usr/src/external/bsd/jemalloc/lib/../dist/src/jemalloc.c:2433
 #9  0x00000001aa403063 in portal_node_reclaim (pu=<optimized out>, opc=0x7ed8ec7b7020) at /usr/src/sbin/mount_portal/puffs_portal.c:812
 #10 0x00007ed8ec008e3b in dispatch (pcc=pcc@entry=0x7ed8ec740000) at /usr/src/lib/libpuffs/dispatcher.c:876
 #11 0x00007ed8ec009495 in puffs__ml_dispatch (pu=0x7ed8ec7ab000, pb=0x7ed8ec795050) at /usr/src/lib/libpuffs/dispatcher.c:64
 #12 0x00007ed8ec00b90e in puffs__framev_input (pu=pu@entry=0x7ed8ec7ab000, fctrl=0x7ed8ec7ab5f8, fio=fio@entry=0x7ed8ec79d060)
     at /usr/src/lib/libpuffs/framebuf.c:699
 #13 0x00007ed8ec00d80b in puffs__theloop (pcc=<optimized out>) at /usr/src/lib/libpuffs/puffs.c:909
 #14 0x00007ed8eb86b3a0 in ?? () from /lib/libc.so.12
 Backtrace stopped: Cannot access memory at address 0x7ed8ec780000