Change cpu_stop_queue_two_works() to ensure that both CPU's have stopper->enabled == T or fail otherwise.
This way stop_two_cpus() no longer needs to check cpu_active() to avoid the deadlock. This patch doesn't remove these checks, we will do this later. Note: we need to take both stopper->lock's at the same time, but this will also help to remove lglock from stop_machine.c, so I hope this is fine. Signed-off-by: Oleg Nesterov <[email protected]> --- kernel/stop_machine.c | 29 ++++++++++++++++++++--------- 1 files changed, 20 insertions(+), 9 deletions(-) diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index 688d6b3..6d85d27 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -219,12 +219,27 @@ static int multi_cpu_stop(void *data) static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1, int cpu2, struct cpu_stop_work *work2) { + struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1); + struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2); + int err; + lg_double_lock(&stop_cpus_lock, cpu1, cpu2); - cpu_stop_queue_work(cpu1, work1); - cpu_stop_queue_work(cpu2, work2); + spin_lock_irq(&stopper1->lock); + spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING); + + err = -ENOENT; + if (!stopper1->enabled || !stopper2->enabled) + goto unlock; + + err = 0; + __cpu_stop_queue_work(stopper1, work1); + __cpu_stop_queue_work(stopper2, work2); +unlock: + spin_unlock(&stopper2->lock); + spin_unlock_irq(&stopper1->lock); lg_double_unlock(&stop_cpus_lock, cpu1, cpu2); - return 0; + return err; } /** * stop_two_cpus - stops two cpus @@ -261,12 +276,8 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void * set_state(&msdata, MULTI_STOP_PREPARE); /* - * If we observe both CPUs active we know _cpu_down() cannot yet have - * queued its stop_machine works and therefore ours will get executed - * first. Or its not either one of our CPUs that's getting unplugged, - * in which case we don't care. - * - * This relies on the stopper workqueues to be FIFO. + * We do not want to migrate to inactive CPU. FIXME: move this + * into the caller. */ if (!cpu_active(cpu1) || !cpu_active(cpu2)) { preempt_enable(); -- 1.5.5.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
