diff options
| author | Oleg Nesterov <oleg@redhat.com> | 2010-03-15 10:10:03 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2010-09-20 13:18:04 -0700 |
| commit | e624a13a60b662d7137fd093c17fd4aa077e1e59 (patch) | |
| tree | 07fd6ce2e764f6c744379bf74a58687b4ae48fbb /kernel/sched.c | |
| parent | 20b622cd1f1a7f557f1587524c75e72f10d8193e (diff) | |
sched: Kill the broken and deadlockable cpuset_lock/cpuset_cpus_allowed_locked code
commit 897f0b3c3ff40b443c84e271bef19bd6ae885195 upstream
This patch just states the fact the cpusets/cpuhotplug interaction is
broken and removes the deadlockable code which only pretends to work.
- cpuset_lock() doesn't really work. It is needed for
cpuset_cpus_allowed_locked() but we can't take this lock in
try_to_wake_up()->select_fallback_rq() path.
- cpuset_lock() is deadlockable. Suppose that a task T bound to CPU takes
callback_mutex. If cpu_down(CPU) happens before T drops callback_mutex
stop_machine() preempts T, then migration_call(CPU_DEAD) tries to take
cpuset_lock() and hangs forever because CPU is already dead and thus
T can't be scheduled.
- cpuset_cpus_allowed_locked() is deadlockable too. It takes task_lock()
which is not irq-safe, but try_to_wake_up() can be called from irq.
Kill them, and change select_fallback_rq() to use cpu_possible_mask, like
we currently do without CONFIG_CPUSETS.
Also, with or without this patch, with or without CONFIG_CPUSETS, the
callers of select_fallback_rq() can race with each other or with
set_cpus_allowed() pathes.
The subsequent patches try to to fix these problems.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100315091003.GA9123@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'kernel/sched.c')
| -rw-r--r-- | kernel/sched.c | 10 |
1 files changed, 3 insertions, 7 deletions
diff --git a/kernel/sched.c b/kernel/sched.c index 92cf8db23767..080b78726872 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2349,11 +2349,9 @@ static int select_fallback_rq(int cpu, struct task_struct *p) return dest_cpu; /* No more Mr. Nice Guy. */ - if (dest_cpu >= nr_cpu_ids) { - rcu_read_lock(); - cpuset_cpus_allowed_locked(p, &p->cpus_allowed); - rcu_read_unlock(); - dest_cpu = cpumask_any_and(cpu_active_mask, &p->cpus_allowed); + if (unlikely(dest_cpu >= nr_cpu_ids)) { + cpumask_copy(&p->cpus_allowed, cpu_possible_mask); + dest_cpu = cpumask_any(cpu_active_mask); /* * Don't tell them about moving exiting tasks or @@ -7833,7 +7831,6 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu) case CPU_DEAD: case CPU_DEAD_FROZEN: - cpuset_lock(); /* around calls to cpuset_cpus_allowed_lock() */ migrate_live_tasks(cpu); rq = cpu_rq(cpu); /* Idle task back to normal (off runqueue, low prio) */ @@ -7844,7 +7841,6 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu) rq->idle->sched_class = &idle_sched_class; migrate_dead_tasks(cpu); spin_unlock_irq(&rq->lock); - cpuset_unlock(); migrate_nr_uninterruptible(rq); BUG_ON(rq->nr_running != 0); calc_global_load_remove(rq); |