From b17718d02f54b90978d0e0146368b512b11c3e84 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 5 Jun 2015 17:30:23 +0200 Subject: sched/stop_machine: Fix deadlock between multiple stop_two_cpus() Jiri reported a machine stuck in multi_cpu_stop() with migrate_swap_stop() as function and with the following src,dst cpu pairs: {11, 4} {13, 11} { 4, 13} 4 11 13 cpuM: queue(4 ,13) *Ma cpuN: queue(13,11) *N Na *M Mb cpuO: queue(11, 4) *O Oa *Nb *Ob Where *X denotes the cpu running the queueing of cpu-X and X[ab] denotes the first/second queued work. You'll observe the top of the workqueue for each cpu: 4,11,13 to be work from cpus: M, O, N resp. IOW. deadlock. Do away with the queueing trickery and introduce lg_double_lock() to lock both CPUs and fully serialize the stop_two_cpus() callers instead of the partial (and buggy) serialization we have now. Reported-by: Jiri Olsa Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Borislav Petkov Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Rik van Riel Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20150605153023.GH19282@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar --- kernel/locking/lglock.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) (limited to 'kernel/locking') diff --git a/kernel/locking/lglock.c b/kernel/locking/lglock.c index 86ae2aebf004..951cfcd10b4a 100644 --- a/kernel/locking/lglock.c +++ b/kernel/locking/lglock.c @@ -60,6 +60,28 @@ 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; -- cgit v1.2.3-58-ga151