Author: jtl Date: Thu Jun 8 20:47:18 2017 New Revision: 319720 URL: https://svnweb.freebsd.org/changeset/base/319720
Log: With EARLY_AP_STARTUP enabled, we are seeing crashes in softclock_call_cc() during bootup. Debugging information shows that softclock_call_cc() is trying to execute the vt_consdev.vd_timer callout, and the callout structure contains a NULL c_func. This appears to be due to a race between vt_upgrade() running callout_reset() and vt_resume_flush_timer() calling callout_schedule(). Fix the race by ensuring that vd_timer_armed is always set before attempting to (re)schedule the callout. Discussed with: emaste MFC after: 2 weeks Sponsored by: Netflix Differential Revision: https://reviews.freebsd.org/D9828 Modified: head/sys/dev/vt/vt_core.c Modified: head/sys/dev/vt/vt_core.c ============================================================================== --- head/sys/dev/vt/vt_core.c Thu Jun 8 20:41:28 2017 (r319719) +++ head/sys/dev/vt/vt_core.c Thu Jun 8 20:47:18 2017 (r319720) @@ -2610,10 +2610,17 @@ vt_upgrade(struct vt_device *vd) /* Init 25 Hz timer. */ callout_init_mtx(&vd->vd_timer, &vd->vd_lock, 0); - /* Start timer when everything ready. */ + /* + * Start timer when everything ready. + * Note that the operations here are purposefully ordered. + * We need to ensure vd_timer_armed is non-zero before we set + * the VDF_ASYNC flag. That prevents this function from + * racing with vt_resume_flush_timer() to update the + * callout structure. + */ + atomic_add_acq_int(&vd->vd_timer_armed, 1); vd->vd_flags |= VDF_ASYNC; callout_reset(&vd->vd_timer, hz / VT_TIMERFREQ, vt_timer, vd); - vd->vd_timer_armed = 1; register_handlers = 1; } _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
