From 4c6c4e38c4e9a454889298dcc498174968d14a09 Mon Sep 17 00:00:00 2001 From: Kirill Tkhai Date: Thu, 6 Mar 2014 13:32:01 +0400 Subject: [PATCH] sched/core: Fix endless loop in pick_next_task() 1) Single cpu machine case. When rq has only RT tasks, but no one of them can be picked because of throttling, we enter in endless loop. pick_next_task_{dl,rt} return NULL. In pick_next_task_fair() we permanently go to retry if (rq->nr_running != rq->cfs.h_nr_running) return RETRY_TASK; (rq->nr_running is not being decremented when rt_rq becomes throttled). No chances to unthrottle any rt_rq or to wake fair here, because of rq is locked permanently and interrupts are disabled. 2) In case of SMP this can cause a hang too. Although we unlock rq in idle_balance(), interrupts are still disabled. The solution is to check for available tasks in DL and RT classes instead of checking for sum. Signed-off-by: Kirill Tkhai Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/1394098321.19290.11.camel@tkhai Signed-off-by: Ingo Molnar --- Reading git-format-patch failed