[PATCH for v4.9 LTS 84/87] signal: protect SIGNAL_UNKILLABLE from unintentional clearing.

From: Jamie Iles [ Upstream commit 2d39b3cd34e6d323720d4c61bd714f5ae202c022 ] Since commit 00cd5c37afd5 ("ptrace: permit ptracing of /sbin/init") we can now trace init processes. init is initially protected with SIGNAL_UNKILLABLE which will prevent fatal signals such as

[PATCH for v4.9 LTS 84/87] signal: protect SIGNAL_UNKILLABLE from unintentional clearing.

From: Jamie Iles [ Upstream commit 2d39b3cd34e6d323720d4c61bd714f5ae202c022 ] Since commit 00cd5c37afd5 ("ptrace: permit ptracing of /sbin/init") we can now trace init processes. init is initially protected with SIGNAL_UNKILLABLE which will prevent fatal signals such as SIGSTOP, but there are