Avoid deadlock when switching task policy to BACKGROUND (ugly)wip-master-2.6.33-rt

When (re)setting Litmus task policy to BACKGROUND, kfree is called while in atomic context. This cannot be done in PreemptRT as it will deadlock (this commit fixes the below trace). Properly freeing rt-task structures while not holding proper locks breaks various assumptions in the code and therefore these operations cannot be easily postponed (to a moment when we don't hold the locks). The solution is a bad hack and if the policy is reset to BACKGROUND task we leak some memory. Better solutions are very welcomed. [ 52.850018] ======================================================= [ 52.850018] [ INFO: possible circular locking dependency detected ] [ 52.850018] 2.6.33.5-rt22-litmus2010 #441 [ 52.850018] ------------------------------------------------------- [ 52.850018] longtest_g/1637 is trying to acquire lock: [ 52.850018] (per_cpu__lock_slab_locked){......}, at: [<ffffffff8142b783>] rt_spin_lock_slowlock+0x33/0x360 [ 52.850018] [ 52.850018] but task is already holding lock: [ 52.850018] (&rq->lock){-...-.}, at: [<ffffffff8102ee52>] __sched_setscheduler+0x112/0x4f0 [ 52.850018] [ 52.850018] which lock already depends on the new lock. [ 52.850018] [ 52.850018] [ 52.850018] the existing dependency chain (in reverse order) is: [ 52.850018] [ 52.850018] -> #2 (&rq->lock){-...-.}: [ 52.850018] [<ffffffff81060954>] __lock_acquire+0x13c4/0x1cd0 [ 52.850018] [<ffffffff810612bc>] lock_acquire+0x5c/0x80 [ 52.850018] [<ffffffff8142cc76>] _raw_spin_lock+0x36/0x50 [ 52.850018] [<ffffffff8102551e>] task_rq_lock+0x5e/0xb0 [ 52.850018] [<ffffffff8102fa44>] try_to_wake_up+0x64/0x420 [ 52.850018] [<ffffffff8102fe65>] wake_up_process_mutex+0x15/0x20 [ 52.850018] [<ffffffff8106708e>] wakeup_next_waiter+0x9e/0x1b0 [ 52.850018] [<ffffffff8142b70f>] rt_spin_lock_slowunlock+0x4f/0x90 [ 52.850018] [<ffffffff8142c419>] rt_spin_unlock+0x49/0x50 [ 52.850018] [<ffffffff8102ceb4>] complete+0x44/0x50 [ 52.850018] [<ffffffff8104d07c>] kthread+0x7c/0xc0 [ 52.850018] [<ffffffff81003214>] kernel_thread_helper+0x4/0x10 [ 52.850018] [ 52.850018] -> #1 (&p->pi_lock){......}: [ 52.850018] [<ffffffff81060954>] __lock_acquire+0x13c4/0x1cd0 [ 52.850018] [<ffffffff810612bc>] lock_acquire+0x5c/0x80 [ 52.850018] [<ffffffff8142cc76>] _raw_spin_lock+0x36/0x50 [ 52.850018] [<ffffffff81066859>] task_blocks_on_rt_mutex+0x39/0x210 [ 52.850018] [<ffffffff8142b9c3>] rt_spin_lock_slowlock+0x273/0x360 [ 52.850018] [<ffffffff8142c383>] rt_spin_lock+0x43/0x90 [ 52.850018] [<ffffffff810ab23e>] _slab_irq_disable+0x4e/0x70 [ 52.850018] [<ffffffff810ab93f>] kmem_cache_free+0x1f/0xf0 [ 52.850018] [<ffffffff810b34a1>] file_free_rcu+0x31/0x40 [ 52.850018] [<ffffffff81074a48>] __rcu_process_callbacks+0x128/0x3a0 [ 52.850018] [<ffffffff81074d3b>] rcu_process_callbacks+0x7b/0x90 [ 52.850018] [<ffffffff8103a96f>] run_ksoftirqd+0x14f/0x310 [ 52.850018] [<ffffffff8104d0a6>] kthread+0xa6/0xc0 [ 52.850018] [<ffffffff81003214>] kernel_thread_helper+0x4/0x10 [ 52.850018] [ 52.850018] -> #0 (per_cpu__lock_slab_locked){......}: [ 52.850018] [<ffffffff8106120c>] __lock_acquire+0x1c7c/0x1cd0 [ 52.850018] [<ffffffff810612bc>] lock_acquire+0x5c/0x80 [ 52.850018] [<ffffffff8142cd91>] _raw_spin_lock_irqsave+0x41/0x60 [ 52.850018] [<ffffffff8142b783>] rt_spin_lock_slowlock+0x33/0x360 [ 52.850018] [<ffffffff8142c383>] rt_spin_lock+0x43/0x90 [ 52.850018] [<ffffffff810ab23e>] _slab_irq_disable+0x4e/0x70 [ 52.850018] [<ffffffff810ab93f>] kmem_cache_free+0x1f/0xf0 [ 52.850018] [<ffffffff811d1374>] litmus_exit_task+0x84/0x130 [ 52.850018] [<ffffffff8102f11f>] __sched_setscheduler+0x3df/0x4f0 [ 52.850018] [<ffffffff8102f24e>] sched_setscheduler+0xe/0x10 [ 52.850018] [<ffffffff8102f30d>] do_sched_setscheduler+0xbd/0x100 [ 52.850018] [<ffffffff8102f384>] sys_sched_setscheduler+0x14/0x20 [ 52.850018] [<ffffffff8100246b>] system_call_fastpath+0x16/0x1b [ 52.850018] [ 52.850018] other info that might help us debug this: [ 52.850018] [ 52.850018] 3 locks held by longtest_g/1637: [ 52.850018] #0: (rcu_read_lock){.+.+..}, at: [<ffffffff8102f2bf>] do_sched_setscheduler+0x6f/0x100 [ 52.850018] #1: (&p->pi_lock){......}, at: [<ffffffff8102ee0e>] __sched_setscheduler+0xce/0x4f0 [ 52.850018] #2: (&rq->lock){-...-.}, at: [<ffffffff8102ee52>] __sched_setscheduler+0x112/0x4f0 [ 52.850018] [ 52.850018] stack backtrace: [ 52.850018] Pid: 1637, comm: longtest_g Tainted: G W 2.6.33.5-rt22-litmus2010 #441 [ 52.850018] Call Trace: [ 52.850018] [<ffffffff8105ef10>] print_circular_bug+0x100/0x110 [ 52.850018] [<ffffffff8106120c>] __lock_acquire+0x1c7c/0x1cd0 [ 52.850018] [<ffffffff81429659>] ? printk+0x67/0x69 [ 52.850018] [<ffffffff8100246b>] ? system_call_fastpath+0x16/0x1b [ 52.850018] [<ffffffff8100246b>] ? system_call_fastpath+0x16/0x1b [ 52.850018] [<ffffffff810612bc>] lock_acquire+0x5c/0x80 [ 52.850018] [<ffffffff8142b783>] ? rt_spin_lock_slowlock+0x33/0x360 [ 52.850018] [<ffffffff8142cd91>] _raw_spin_lock_irqsave+0x41/0x60 [ 52.850018] [<ffffffff8142b783>] ? rt_spin_lock_slowlock+0x33/0x360 [ 52.850018] [<ffffffff81005649>] ? dump_trace+0x129/0x330 [ 52.850018] [<ffffffff8142b783>] rt_spin_lock_slowlock+0x33/0x360 [ 52.850018] [<ffffffff8142c383>] rt_spin_lock+0x43/0x90 [ 52.850018] [<ffffffff810ab23e>] _slab_irq_disable+0x4e/0x70 [ 52.850018] [<ffffffff810ab93f>] kmem_cache_free+0x1f/0xf0 [ 52.850018] [<ffffffff811d1374>] litmus_exit_task+0x84/0x130 [ 52.850018] [<ffffffff810242d8>] ? dequeue_task+0x48/0x90 [ 52.850018] [<ffffffff8102f11f>] __sched_setscheduler+0x3df/0x4f0 [ 52.850018] [<ffffffff8102f24e>] sched_setscheduler+0xe/0x10 [ 52.850018] [<ffffffff8102f30d>] do_sched_setscheduler+0xbd/0x100 [ 52.850018] [<ffffffff8102f2bf>] ? do_sched_setscheduler+0x6f/0x100 [ 52.850018] [<ffffffff8142bf02>] ? trace_hardirqs_on_thunk+0x3a/0x3f [ 52.850018] [<ffffffff8102f384>] sys_sched_setscheduler+0x14/0x20 [ 52.850018] [<ffffffff8100246b>] system_call_fastpath+0x16/0x1b
author: Andrea Bastoni <bastoni@cs.unc.edu> 2010-06-10 13:24:54 -0400
committer: Andrea Bastoni <bastoni@cs.unc.edu> 2010-06-10 13:24:54 -0400
commit: 53d9688562a712a9b3e0265b51f2e60fec103799 (patch)
tree: c525e4527e4e3c85d1818389257de8f1ebd6c78c /kernel/sched.c
parent: 5980b2330359d002e4e2278327ff80307504b848 (diff)
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 0166daa4a374..5969c8b25689 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -905,7 +905,7 @@ static __read_mostly int scheduler_running;
 *
 * Litmus RT: with the Preempt-RT patch we rely on rt-threads
 * to set timers. If the RT throttling gets activated we experience
- * very long latencies. Change from 950000 to -1 -> RUNTIME_INF 
+ * very long latencies. Change from 950000 to -1 -> RUNTIME_INF
 */
 int sysctl_sched_rt_runtime = -1;
@@ -6805,7 +6805,7 @@ recheck:
        p->sched_reset_on_fork = reset_on_fork;
        if (p->policy == SCHED_LITMUS)
-                litmus_exit_task(p);
+                litmus_exit_task(p, 0);
        oldprio = p->prio;
        prev_class = p->sched_class;
author	Andrea Bastoni <bastoni@cs.unc.edu>	2010-06-10 13:24:54 -0400
committer	Andrea Bastoni <bastoni@cs.unc.edu>	2010-06-10 13:24:54 -0400
commit	53d9688562a712a9b3e0265b51f2e60fec103799 (patch)
tree	c525e4527e4e3c85d1818389257de8f1ebd6c78c /kernel/sched.c
parent	5980b2330359d002e4e2278327ff80307504b848 (diff)

diff --git a/kernel/sched.c b/kernel/sched.c index 0166daa4a374..5969c8b25689 100644 --- a/kernel/sched.c +++ b/kernel/sched.c
@@ -905,7 +905,7 @@ static __read_mostly int scheduler_running;
905	*	905	*
906	* Litmus RT: with the Preempt-RT patch we rely on rt-threads	906	* Litmus RT: with the Preempt-RT patch we rely on rt-threads
907	* to set timers. If the RT throttling gets activated we experience	907	* to set timers. If the RT throttling gets activated we experience
908	* very long latencies. Change from 950000 to -1 -> RUNTIME_INF	908	* very long latencies. Change from 950000 to -1 -> RUNTIME_INF
909	*/	909	*/
910	int sysctl_sched_rt_runtime = -1;	910	int sysctl_sched_rt_runtime = -1;
911		911
@@ -6805,7 +6805,7 @@ recheck:
6805	p->sched_reset_on_fork = reset_on_fork;	6805	p->sched_reset_on_fork = reset_on_fork;
6806		6806
6807	if (p->policy == SCHED_LITMUS)	6807	if (p->policy == SCHED_LITMUS)
6808	litmus_exit_task(p);	6808	litmus_exit_task(p, 0);
6809		6809
6810	oldprio = p->prio;	6810	oldprio = p->prio;
6811	prev_class = p->sched_class;	6811	prev_class = p->sched_class;