svn commit: r328320 - head/sys/kern

[Wojciech Macek]

Author: wma
Date: Wed Jan 24 07:54:05 2018
New Revision: 328320
URL: https://svnweb.freebsd.org/changeset/base/328320

Log:
  ULE: provide defaults to ts_cpu
  
  Fix a bug when the system has no CPU 0. When created, threads were implicitly assigned to CPU 0.
  This had no practical effect since a real CPU was chosen immediately by the scheduler. However,
  on systems without a CPU 0, sched_ule attempted to access the scheduler queue of the "old" CPU
  when assigned the initial choice of the old one. This caused an attempt to use illegal memory
  and a crash (or, more usually, a deadlock). Fix this by assigned new threads to the BSP
  explicitly and add some asserts to see that this problem does not recur.
  
  Authored by:           Nathan Whitehorn <nwhitehorn at freebsd.org>
  Submitted by:          Wojciech Macek <wma at semihalf.com>
  Obtained from:         Semihalf
  Differential revision: https://reviews.freebsd.org/D13932

Modified:
  head/sys/kern/sched_ule.c

Modified: head/sys/kern/sched_ule.c
==============================================================================
--- head/sys/kern/sched_ule.c	Wed Jan 24 07:01:44 2018	(r328319)
+++ head/sys/kern/sched_ule.c	Wed Jan 24 07:54:05 2018	(r328320)
@@ -1405,6 +1405,7 @@ sched_setup(void *dummy)
 
 	/* Add thread0's load since it's running. */
 	TDQ_LOCK(tdq);
+	td_get_sched(&thread0)->ts_cpu = curcpu; /* Something valid to start */
 	thread0.td_lock = TDQ_LOCKPTR(TDQ_SELF());
 	tdq_load_add(tdq, &thread0);
 	tdq->tdq_lowpri = thread0.td_priority;
@@ -2454,6 +2455,7 @@ sched_add(struct thread *td, int flags)
 	 * Pick the destination cpu and if it isn't ours transfer to the
 	 * target cpu.
 	 */
+	td_get_sched(td)->ts_cpu = curcpu; /* Pick something valid to start */
 	cpu = sched_pickcpu(td, flags);
 	tdq = sched_setcpu(td, cpu, flags);
 	tdq_add(tdq, td, flags);