proc/threads_stack: no need in this patch, we can use /proc/PID/maps+xargs

With this patch:
$ grep Threads /proc/*/status | grep -v '1$' | cut -d: -f1 | sed 's/status/threads_stack/' | xargs cat
[<ffffffff81134242>] poll_schedule_timeout+0x3c/0x5c
[<ffffffff81134c86>] do_select+0x60a/0x64c
[<ffffffff81134e51>] core_sys_select+0x189/0x241
[<ffffffff81134f8d>] SyS_select+0x84/0xba
[<ffffffff813cc862>] system_call_fastpath+0x16/0x1b
[<ffffffffffffffff>] 0xffffffffffffffff

[<ffffffff810769c6>] do_syslog+0x125/0x470
[<ffffffff8117e02f>] kmsg_read+0x28/0x4f
[<ffffffff81173814>] proc_reg_read+0x55/0x77
[<ffffffff8112580c>] vfs_read+0x8a/0xee
[<ffffffff81125fc8>] SyS_read+0x41/0x76
[<ffffffff813cc862>] system_call_fastpath+0x16/0x1b
[<ffffffffffffffff>] 0xffffffffffffffff

[<ffffffff8108af49>] futex_wait_queue_me+0xd7/0x134
[<ffffffff8108b47c>] futex_wait+0x119/0x24f
[<ffffffff8108c799>] do_futex+0x9c/0x787
[<ffffffff8108cf3d>] SyS_futex+0xb9/0x12b
[<ffffffff813cc862>] system_call_fastpath+0x16/0x1b
[<ffffffffffffffff>] 0xffffffffffffffff

Without:
$ grep Threads /proc/*/status | grep -v '1$' | cut -d: -f1 | sed 's/status/maps/' | xargs grep stack: | cut -d: -f3 | tr -d ] | sort -n | xargs -I{} sh -c "cat /proc/{}/stack && echo"
[<ffffffff81134242>] poll_schedule_timeout+0x3c/0x5c
[<ffffffff81134c86>] do_select+0x60a/0x64c
[<ffffffff81134e51>] core_sys_select+0x189/0x241
[<ffffffff81134f8d>] SyS_select+0x84/0xba
[<ffffffff813cc862>] system_call_fastpath+0x16/0x1b
[<ffffffffffffffff>] 0xffffffffffffffff

[<ffffffff810769c6>] do_syslog+0x125/0x470
[<ffffffff8117e02f>] kmsg_read+0x28/0x4f
[<ffffffff81173814>] proc_reg_read+0x55/0x77
[<ffffffff8112580c>] vfs_read+0x8a/0xee
[<ffffffff81125fc8>] SyS_read+0x41/0x76
[<ffffffff813cc862>] system_call_fastpath+0x16/0x1b
[<ffffffffffffffff>] 0xffffffffffffffff

[<ffffffff8108af49>] futex_wait_queue_me+0xd7/0x134
[<ffffffff8108b47c>] futex_wait+0x119/0x24f
[<ffffffff8108c799>] do_futex+0x9c/0x787
[<ffffffff8108cf3d>] SyS_futex+0xb9/0x12b
[<ffffffff813cc862>] system_call_fastpath+0x16/0x1b
[<ffffffffffffffff>] 0xffffffffffffffff