From: Michael wang Date: Thu, 20 Feb 2014 03:14:53 +0000 (+0800) Subject: sched/fair: Reset se-depth when task switched to FAIR X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=eb7a59b2c888c2518ba2c9d0020343ca71aa9dee;p=openwrt%2Fstaging%2Fblogic.git sched/fair: Reset se-depth when task switched to FAIR Sasha reported: [ 522.645288] BUG: unable to handle kernel NULL pointer dereference at ... [ 522.646271] IP: [] check_preempt_wakeup+0x11f/0x210 ... [ 522.650021] Call Trace: [ 522.650021] [ 522.650021] [] check_preempt_curr+0x3d/0xb0 [ 522.650021] [] ttwu_do_wakeup+0x18/0x130 ... which was caused by the se-depth changed during the time when task is not FAIR, and we will use the wrong depth value after it switched back to FAIR. This patch reset the depth at the time when task switched to FAIR, make sure that we always have the correct value when task is FAIR. Cc: Ingo Molnar Reported-by: Sasha Levin Tested-by: Sasha Levin Signed-off-by: Michael Wang Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/5305732D.70001@linux.vnet.ibm.com Signed-off-by: Thomas Gleixner --- diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 235cfa7ad8fc..280da893cd0f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7317,7 +7317,15 @@ static void switched_from_fair(struct rq *rq, struct task_struct *p) */ static void switched_to_fair(struct rq *rq, struct task_struct *p) { - if (!p->se.on_rq) + struct sched_entity *se = &p->se; +#ifdef CONFIG_FAIR_GROUP_SCHED + /* + * Since the real-depth could have been changed (only FAIR + * class maintain depth value), reset depth properly. + */ + se->depth = se->parent ? se->parent->depth + 1 : 0; +#endif + if (!se->on_rq) return; /*