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stop_machine: Remove stop_cpus_lock and lg_double_lock/unlock()

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stop_two_cpus() and stop_cpus() use stop_cpus_lock to avoid the deadlock,
we need to ensure that the stopper functions can't be queued "backwards"
from one another. This doesn't look nice; if we use lglock then we do not
really need stopper->lock, cpu_stop_queue_work() could use lg_local_lock()
under local_irq_save().

OTOH it would be even better to avoid lglock in stop_machine.c and remove
lg_double_lock(). This patch adds "bool stop_cpus_in_progress" set/cleared
by queue_stop_cpus_work(), and changes cpu_stop_queue_two_works() to busy
wait until it is cleared.

queue_stop_cpus_work() sets stop_cpus_in_progress = T lockless, but after
it queues a work on CPU1 it must be visible to stop_two_cpus(CPU1, CPU2)
which checks it under the same lock. And since stop_two_cpus() holds the
2nd lock too, queue_stop_cpus_work() can not clear stop_cpus_in_progress
if it is also going to queue a work on CPU2, it needs to take that 2nd
lock to do this.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20151121181148.GA433@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Oleg Nesterov
2015-11-21 19:11:48 +01:00
committed by Ingo Molnar
parent 87709e28dc
commit e625397041
3 changed files with 26 additions and 43 deletions
Download Patch File Download Diff File Expand all files Collapse all files
kernel/locking/lglock.c
-22
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@@ -60,28 +60,6 @@ void lg_local_unlock_cpu(struct lglock *lg, int cpu)
}
EXPORT_SYMBOL(lg_local_unlock_cpu);
void lg_double_lock(struct lglock *lg, int cpu1, int cpu2)
{
BUG_ON(cpu1 == cpu2);
/* lock in cpu order, just like lg_global_lock */
if (cpu2 < cpu1)
swap(cpu1, cpu2);
preempt_disable();
lock_acquire_shared(&lg->lock_dep_map, 0, 0, NULL, _RET_IP_);
arch_spin_lock(per_cpu_ptr(lg->lock, cpu1));
arch_spin_lock(per_cpu_ptr(lg->lock, cpu2));
}
void lg_double_unlock(struct lglock *lg, int cpu1, int cpu2)
{
lock_release(&lg->lock_dep_map, 1, _RET_IP_);
arch_spin_unlock(per_cpu_ptr(lg->lock, cpu1));
arch_spin_unlock(per_cpu_ptr(lg->lock, cpu2));
preempt_enable();
}
void lg_global_lock(struct lglock *lg)
{
int i;