Author: markj Date: Thu Dec 12 02:43:24 2019 New Revision: 355644 URL: https://svnweb.freebsd.org/changeset/base/355644
Log: 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 Modified: head/sys/kern/sched_ule.c Modified: head/sys/kern/sched_ule.c ============================================================================== --- head/sys/kern/sched_ule.c Thu Dec 12 02:42:27 2019 (r355643) +++ head/sys/kern/sched_ule.c Thu Dec 12 02:43:24 2019 (r355644) @@ -244,7 +244,7 @@ struct tdq { volatile short tdq_switchcnt; /* Switches this tick. */ volatile short tdq_oldswitchcnt; /* Switches last tick. */ u_char tdq_lowpri; /* Lowest priority thread. */ - u_char tdq_ipipending; /* IPI pending. */ + u_char tdq_owepreempt; /* Remote preemption pending. */ u_char tdq_idx; /* Current insert index. */ u_char tdq_ridx; /* Current removal index. */ int tdq_id; /* cpuid. */ @@ -1073,7 +1073,7 @@ tdq_notify(struct tdq *tdq, struct thread *td) int pri; int cpu; - if (tdq->tdq_ipipending) + if (tdq->tdq_owepreempt) return; cpu = td_get_sched(td)->ts_cpu; pri = td->td_priority; @@ -1096,7 +1096,12 @@ tdq_notify(struct tdq *tdq, struct thread *td) if (!tdq->tdq_cpu_idle || cpu_idle_wakeup(cpu)) return; } - tdq->tdq_ipipending = 1; + + /* + * The run queues have been updated, so any switch on the remote CPU + * will satisfy the preemption request. + */ + tdq->tdq_owepreempt = 1; ipi_cpu(cpu, IPI_PREEMPT); } @@ -2079,8 +2084,10 @@ sched_switch(struct thread *td, struct thread *newtd, (flags & SW_PREEMPT) != 0; td->td_flags &= ~(TDF_NEEDRESCHED | TDF_SLICEEND); td->td_owepreempt = 0; + tdq->tdq_owepreempt = 0; if (!TD_IS_IDLETHREAD(td)) tdq->tdq_switchcnt++; + /* * The lock pointer in an idle thread should never change. Reset it * to CAN_RUN as well. @@ -2386,7 +2393,6 @@ sched_preempt(struct thread *td) thread_lock(td); tdq = TDQ_SELF(); TDQ_LOCK_ASSERT(tdq, MA_OWNED); - tdq->tdq_ipipending = 0; if (td->td_priority > tdq->tdq_lowpri) { int flags; @@ -2397,6 +2403,8 @@ sched_preempt(struct thread *td) mi_switch(flags | SWT_REMOTEWAKEIDLE, NULL); else mi_switch(flags | SWT_REMOTEPREEMPT, NULL); + } else { + tdq->tdq_owepreempt = 0; } thread_unlock(td); } _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
