From: Chris Metcalf Date: Thu, 15 Oct 2015 19:35:34 +0000 (-0400) Subject: arch/tile: turn off timer tick for oneshot_stopped state X-Git-Tag: KARO-TX6UL-2015-11-03~119^2 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=09745f38a74eb2e5bb65dd49e7c225cd5180e932;p=karo-tx-linux.git arch/tile: turn off timer tick for oneshot_stopped state When the schedule tick is disabled in tick_nohz_stop_sched_tick(), we call hrtimer_cancel(), which eventually calls down into __remove_hrtimer() and thus into hrtimer_force_reprogram(). That function's call to tick_program_event() detects that we are trying to set the expiration to KTIME_MAX and calls clockevents_switch_state() to set the state to ONESHOT_STOPPED, and returns. However, by default the internal __clockevents_switch_state() code doesn't have a "set_state_oneshot_stopped" function pointer for the tile clock_event_device, so that code returns -ENOSYS, and we end up not setting the state, and more importantly, we don't actually turn off the tile hardware timer. As a result, the timer tick we were waiting for before is still queued, and fires shortly afterwards, only to discover there was nothing for it to do, at which point it quiesces. The fix is to provide that function pointer for tile, and like the other function pointers, have it just turn off the timer interrupt. Any call to set a new timer interval will properly re-enable it. This fix avoids a small performance hiccup for regular applications, but for TASK_ISOLATION code, it fixes a potentially disastrous kernel timer interruption that could cause packets to be dropped. Signed-off-by: Chris Metcalf --- diff --git a/arch/tile/kernel/time.c b/arch/tile/kernel/time.c index 178989e6d3e3..fbedf380d9d4 100644 --- a/arch/tile/kernel/time.c +++ b/arch/tile/kernel/time.c @@ -159,6 +159,7 @@ static DEFINE_PER_CPU(struct clock_event_device, tile_timer) = { .set_next_event = tile_timer_set_next_event, .set_state_shutdown = tile_timer_shutdown, .set_state_oneshot = tile_timer_shutdown, + .set_state_oneshot_stopped = tile_timer_shutdown, .tick_resume = tile_timer_shutdown, };