K 10
svn:author
V 5
markj
K 8
svn:date
V 27
2019-12-12T02:43:24.800365Z
K 7
svn:log
V 817
Rename tdq_ipipending and clear it in sched_switch().

This fixes a regression after r355311.  Specifically, sched_preempt()
may trigger a context switch by calling thread_lock(), since
thread_lock() calls critical_exit() in its slow path and the interrupted
thread may have already been marked for preemption.  This would happen
before tdq_ipipending is cleared, blocking further preemption IPIs.  The
CPU can be left in this state indefinitely if the interrupted thread
migrates.

Rename tdq_ipipending to tdq_owepreempt.  Any switch satisfies a remote
preemption request, so clear tdq_owepreempt in sched_switch() instead of
sched_preempt() to avoid subtle problems of the sort described above.

Reviewed by:	jeff, kib
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D22758

END