From: Thomas Gleixner Date: Tue, 22 May 2007 06:38:50 +0000 (+0200) Subject: [PATCH] Prevent going idle with softirq pending X-Git-Tag: v2.6.21.5~45 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=f7b901ae5dbcacf8808c98e5104e56567600918d;p=karo-tx-linux.git [PATCH] Prevent going idle with softirq pending The NOHZ patch contains a check for softirqs pending when a CPU goes idle. The BUG is unrelated to NOHZ, it just was made visible by the NOHZ patch. The BUG showed up mainly on P4 / hyperthreading enabled machines which lead the investigations into the wrong direction in the first place. The real cause is in cond_resched_softirq(): cond_resched_softirq() is enabling softirqs without invoking the softirq daemon when softirqs are pending. This leads to the warning message in the NOHZ idle code: t1 runs softirq disabled code on CPU#0 interrupt happens, softirq is raised, but deferred (softirqs disabled) t1 calls cond_resched_softirq() enables softirqs via _local_bh_enable() calls schedule() t2 runs t1 is migrated to CPU#1 t2 is done and invokes idle() NOHZ detects the pending softirq Fix: change _local_bh_enable() to local_bh_enable() so the softirq daemon is invoked. Thanks to Anant Nitya for debugging this with great patience ! Signed-off-by: Thomas Gleixner Signed-off-by: Ingo Molnar Signed-off-by: Andrew Morton Cc: Anant Nitya Signed-off-by: Chris Wright Signed-off-by: Greg Kroah-Hartman --- diff --git a/kernel/sched.c b/kernel/sched.c index b9a683730148..a3993b9e7503 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -4545,9 +4545,7 @@ int __sched cond_resched_softirq(void) BUG_ON(!in_softirq()); if (need_resched() && system_state == SYSTEM_RUNNING) { - raw_local_irq_disable(); - _local_bh_enable(); - raw_local_irq_enable(); + local_bh_enable(); __cond_resched(); local_bh_disable(); return 1;