File 0839-Prevent-endless-reschedule-of-sys-task-due... of Package erlang

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File 0839-Prevent-endless-reschedule-of-sys-task-due-to-high-p.patch of Package erlang

From 258e0e7955f99e49f76bb3a66ab2275cc27e45fd Mon Sep 17 00:00:00 2001
From: Rickard Green <rickard@erlang.org>
Date: Wed, 29 Jan 2020 14:30:28 +0100
Subject: [PATCH] Prevent endless reschedule of sys-task due to high prio
 dirty-job

Higher prio dirty-job in combination with lower prio sys-task could
cause an endless rescheduling of the sys-task without making any
progress. This since we refuse to execute on a dirty scheduler if
we got sys-tasks as well as refuse to execute lower prio sys-tasks
if we got other higher prio work to do.

Solved by executing lower prio sys-task even though we got higher
prio dirty-jobs. This since it is non-trivial to reschedule already
scheduled sys-tasks for handling while executing dirty and we do
not now how long time it takes until we return from dirty work.
---
 erts/emulator/beam/erl_process.c     |  8 ++++++--
 erts/emulator/test/process_SUITE.erl | 15 +++++++++++++--
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/erts/emulator/beam/erl_process.c b/erts/emulator/beam/erl_process.c
index 9f6adb03d0..42a310d60a 100644
--- a/erts/emulator/beam/erl_process.c
+++ b/erts/emulator/beam/erl_process.c
@@ -11077,10 +11077,14 @@ fetch_sys_task(Process *c_p, erts_aint32_t state, int *qmaskp, int *priop)
 
     qmask = c_p->sys_task_qs->qmask;
 
-    if ((state & (ERTS_PSFLG_ACTIVE
+    if ((state & (ERTS_PSFLGS_DIRTY_WORK
+                  | ERTS_PSFLG_ACTIVE
 		  | ERTS_PSFLG_EXITING
 		  | ERTS_PSFLG_SUSPENDED)) == ERTS_PSFLG_ACTIVE) {
-	/* No sys tasks if we got exclusively higher prio user work to do */
+	/*
+         * No sys tasks if we got exclusively higher prio user work
+         * to do; ignoring dirty work...
+         */
 	st = NULL;
 	switch (ERTS_PSFLGS_GET_USR_PRIO(state)) {
 	case PRIORITY_MAX:
diff --git a/erts/emulator/test/process_SUITE.erl b/erts/emulator/test/process_SUITE.erl
index a8bcfac84d..8b3e85e9f0 100644
--- a/erts/emulator/test/process_SUITE.erl
+++ b/erts/emulator/test/process_SUITE.erl
@@ -62,7 +62,8 @@
 	 system_task_on_suspended/1,
          system_task_failed_enqueue/1,
 	 gc_request_when_gc_disabled/1,
-	 gc_request_blast_when_gc_disabled/1]).
+	 gc_request_blast_when_gc_disabled/1,
+         otp_16436/1]).
 -export([prio_server/2, prio_client/2, init/1, handle_event/2]).
 
 -export([init_per_testcase/2, end_per_testcase/2]).
@@ -110,7 +111,8 @@ groups() ->
      {system_task, [],
       [no_priority_inversion, no_priority_inversion2,
        system_task_blast, system_task_on_suspended, system_task_failed_enqueue,
-       gc_request_when_gc_disabled, gc_request_blast_when_gc_disabled]}].
+       gc_request_when_gc_disabled, gc_request_blast_when_gc_disabled,
+       otp_16436]}].
 
 init_per_suite(Config) ->
     A0 = case application:start(sasl) of
@@ -2866,6 +2868,15 @@ gc_request_blast_when_gc_disabled(Config) when is_list(Config) ->
     receive {'DOWN', M, process, P, _Reason} -> ok end,
     ok.
 
+otp_16436(Config) when is_list(Config) ->
+    P = spawn_opt(fun () ->
+                          erts_debug:dirty_io(wait, 1000)
+                  end,
+                  [{priority,high},link]),
+    erlang:check_process_code(P, non_existing),
+    unlink(P),
+    exit(P, kill),
+    ok.
 
 %% Internal functions
 
-- 
2.16.4

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