Hanging ag (textproc/the_silver_searcher) on a tmpfs
====================================================
On NetBSD/amd64 8.99.37 of 2019-04-26, extracting libvirt-5.2.0.tar.xz^[0]
tarball via `bsdtar xJf' and then in libvirt-5.2.0 directory running:

 % ag std

(and probably any other similar ag incantations) leads to an hanging
and unkillable ag process.  Please note that sometimes it doesn't
hang, retrying to invoke ag several times (3-10) then lead to an
hanging ag.

According ^T in tcsh:

 [ 2265.2085545] load: 0.00  cmd: ag 1675 [tstile tstile tstile tstile tstile uao_put tstile parked] 1.01u 0.67s 0% 4136k

In crash(8) we can see:

 crash> ps
 PID    LID S CPU     FLAGS       STRUCT LWP *               NAME WAIT
 [...]
 1675     8 3   4         0   ffff80f5c22165e0                 ag tstile
 1675     7 3   3         0   ffff80f5c22161a0                 ag tstile
 1675     6 3   5         0   ffff80f5c4b67a00                 ag tstile
 1675     5 3   7         0   ffff80f5c4b675c0                 ag tstile
 1675     4 3   3         0   ffff80f5c4b67180                 ag tstile
 1675     3 3   0         0   ffff80f4f84b89e0                 ag uao_put
 1675     2 3   4         0   ffff80f4f84b8160                 ag tstile
 1675     1 3   1        80   ffff80f5f21bb320                 ag parked
 [...]

Inspecting the backtrace of all the threads:

 # echo ps | crash | awk '$1 == 1675 { print "bt/a " $6 }' | crash
 Crash version 8.99.37, image version 8.99.37.
 Output from a running system is unreliable.
 trace: pid 1675 lid 8 at 0xffff9381d5201e20
 sleepq_block() at sleepq_block+0xb8
 turnstile_block() at turnstile_block+0x4f8
 rw_vector_enter() at rw_vector_enter+0x20f
 vm_map_lock() at vm_map_lock+0x66
 sys_munmap() at sys_munmap+0x58
 syscall() at syscall+0x188
 --- syscall (number 73) ---
 72e355b9a1ba:
 trace: pid 1675 lid 7 at 0xffff9381d51fce20
 sleepq_block() at sleepq_block+0xb8
 turnstile_block() at turnstile_block+0x4f8
 rw_vector_enter() at rw_vector_enter+0x20f
 vm_map_lock() at vm_map_lock+0x66
 sys_munmap() at sys_munmap+0x58
 syscall() at syscall+0x188
 --- syscall (number 73) ---
 72e355b9a1ba:
 trace: pid 1675 lid 6 at 0xffff9381d51f7e20
 sleepq_block() at sleepq_block+0xb8
 turnstile_block() at turnstile_block+0x4f8
 rw_vector_enter() at rw_vector_enter+0x20f
 vm_map_lock() at vm_map_lock+0x66
 sys_munmap() at sys_munmap+0x58
 syscall() at syscall+0x188
 --- syscall (number 73) ---
 72e355b9a1ba:
 trace: pid 1675 lid 5 at 0xffff9381d51f2c50
 sleepq_block() at sleepq_block+0xb8
 turnstile_block() at turnstile_block+0x4f8
 rw_vector_enter() at rw_vector_enter+0x20f
 uvm_fault_internal() at uvm_fault_internal+0x1838
 trap() at trap+0x343
 --- trap (number 6) ---
 409248:
 trace: pid 1675 lid 4 at 0xffff9381d51ede20
 sleepq_block() at sleepq_block+0xb8
 turnstile_block() at turnstile_block+0x4f8
 rw_vector_enter() at rw_vector_enter+0x20f
 vm_map_lock() at vm_map_lock+0x66
 sys_munmap() at sys_munmap+0x58
 syscall() at syscall+0x188
 --- syscall (number 73) ---
 72e355b9a1ba:
 trace: pid 1675 lid 3 at 0xffff9381d51e8b30
 sleepq_block() at sleepq_block+0xb8
 mtsleep() at mtsleep+0x149
 uao_put() at uao_put+0x268
 VOP_PUTPAGES() at VOP_PUTPAGES+0x53
 uvm_fault_internal() at uvm_fault_internal+0x1506
 trap() at trap+0x343
 --- trap (number 6) ---
 408e94:
 trace: pid 1675 lid 2 at 0xffff9381d51dee20
 sleepq_block() at sleepq_block+0xb8
 turnstile_block() at turnstile_block+0x4f8
 rw_vector_enter() at rw_vector_enter+0x20f
 vm_map_lock() at vm_map_lock+0x66
 sys_munmap() at sys_munmap+0x58
 syscall() at syscall+0x188
 --- syscall (number 73) ---
 72e355b9a1ba:
 trace: pid 1675 lid 1 at 0xffff9381cbe38ed0
 sleepq_block() at sleepq_block+0xb8
 lwp_park() at lwp_park+0x117
 sys____lwp_park60() at sys____lwp_park60+0x5a
 syscall() at syscall+0x188
 --- syscall (number 478) ---
 72e355ab3d7a:

[0]: http://libvirt.org/sources/libvirt-5.2.0.tar.xz